Basically what pokoko said. There’s a lot more diversity with manga because other genres have had a lot more time to flourish. Sure, you have your One Piece and Dragonball clones everywhere, but if you check periodic Oricon sales you’ll find there’s quite a big audience for other genres. I remember Wotakoi, an SoL rom-com about working adults, recently made the top 3 or 5. Western comics don’t have that same diversity because there just currently isn’t that audience, money talks at the end of the day.

However, it does seem like the stigma of comics/animation being for children seems to be dying off, so it’s possible this mindset will shift over the next few decades. There’s already some nice diverse stuff in the western amateur scene, so it’s more than possible we’ll see popular western equivalents to shoujo/josei content someday.

It might look like that on the surface with comics but it's not. With western animation, that's a different story. Mainly kids shows and stuff that looks like ass like southpark.

it actually has to do with how the western cartoon industry and the manga industry started. in the west, animation has always been held to a high standard by big name companies. look at how long Dianey has been making cartoons, or even WB. then consider the fact that its a capitalist industry and that these companies arent open to trying new things. animation is expensive, and they only want what works. now contrast that to the japanese market which was primarily started to provide struggling families with a form of cheap and easy entertainment after the nukings of Nagasaki and Hiroshima during WWII (not even joking, look it up if you dont believe me). as a result, anybody with a pen and paper was able to draw manga and make a small name for themselves. more people means more ideas, and that led to more diversity.

Agree that is one thing I like about manga over Amerian comics. For example I like Batman and Spider-Man, but I would never be able to read through them because they go on for decades and a whole bunch of different. Whereas the two manga I want to read (Ghost in the Shell and Sanctuary) are much smaller and contained.

For comics, I think western comics are as diverse as manga,you just need to see outside the box of Marvel/DC.

For animations, the thing is that those different types of anime reached the mainstream audience and have its own dedicated fanbase while western animation is still having a hard time leaving the usual market. Big animation channels like Disney, Cartoon Network and Nick invest a lot on their usual comedy shows because that is were the easy money are and it is where they know there is an audience. You can find western animation taking different genres but those usually fall into the "niche audience" kind of thing and hardly reach the mainstream.

Sanctuary is fantastic, best manga I've ever read.

Please show me all the gay couples on Comics, transex, comics about writting comics, comics about playing wheelchair basketball, about hunting for food, mob, cycling, playing go or chess, etc.

At least in Brazil, nothing outside of heroes comics are know, but all these mangas are well know in Brazil.

One of your links is from 2009, another is an old man grumbling about animators, and another actually begins with the line, "The anime industry, while not as strong as it was back in 2004-2006, is still booming."

The simple fact is that anime is growing, mainly due to overseas interest.  

https://www.animenewsnetwork.com/news/2018-04-30/anime-industry-report-shows-continued-growth-in-overseas-market/.130302

"Total revenue from overseas sales, which includes broadcast rights, box office, DVD/Blu-ray sales and merchandising, jumped almost a third to $6.79 billion (￥768 billion) over the previous year. Sales to China increased, an AJA spokesperson confirmed, but figures for individual countries aren't compiled for the report."

https://www.hollywoodreporter.com/news/japans-anime-industry-grows-record-177b-boosted-by-your-name-exports-1058463

The decline you're talking about doesn't exist.  There certainly are problems but there have always been problems.  The outlook, however, is positive.

As far as your idea that Japan needs to change anime to suit the rest of the world, we've already seen that with the gaming industry and it was a failure.  The Japanese gaming industry only began to recover when they stopped trying to copy western trends and returned to doing what they knew best.

Regarding your remarks on diversity, I still get the impression that you're talking about a subject where you know little.  Does anime have big name titles designed to appeal to key demographics?  Of course.  However, saying this means it lacks diversity would be like pointing to a select group of Hollywood movies and pretending nothing else was being produced by the film industry.  Anime pulls from sources designed for little girls, little boys, teenage girls, teenages boy, mature women, and mature men.

Is anime anywhere close to being diverse as manga?  No.  Is it more diverse than western animation?  Yeah.  It typically hits several different genres that are intended for different demographics.

Let's take a look at some of the best anime of last year in visual form:

Not diverse enough for you?  Okay, that's fine.  "The same shit"?  It would seem that you're talking about a subject where you know very little.

Why are Manga more diverse than western comics. The reasons is:
The whole culture in Japan reads Manga, all ages, all genders. Inside a manga shop in Japan, there are a large diversity of the public, not just a nerdy subculture & young males. Manga in Japan is like; Bullrings in Spain, Football in England, Pizzas in Italy; Manga is a part of their cultural identity.
Manga is everywhere in Japan: It's a diverse business because of it's diverse consumers (diverse enough to try to meet the entire nation's tastes).
There are also diverse western comics too, but you'll have to go out of your own way to find them. Whereas If you lived in Japan, you would see any niche manga being advertised everywhere on street screens, posters, billboards, TV Ads, shop windows, etc.

People say this, but I don't think it's true in the least bit. There will never be a western comic about, for instance, making a dictionary.

Japan is way more open to a variety of demographic, genre, and story structures when it comes to their comics. Whereas western comics will pretty much always focus on the main comic-buying demographic, leaving very little for anything else, and it shows in terms of the lack of diversity in western comics.

I wonder if a big part of it is the fact that manga is black and white and (from what I've seen) generally printed on cheap paper.

Comic books are a lot more expensive to make, and that makes publishers more risk averse. It also would I imagine make readers a bit less likely to try new or weird things. Comics are about $4 an issue for about 20 pages. Getting into a series can be an investment.

Then there's also logistical difficulties. The US has a far more spread out population, and distributing books across 50 states again makes the process more expensive.