What about third party games that suddenly become first party?

You want all third party games to go everywhere - but would you support a company to spend billions to buy out a publisher thus removing third part games?
What about games like VR? Ones that can't come to all platforms but not all platforms support them.
What about companies that aren't large enough to develop and port a game for all platforms?
What about "third party" games that never go to any other platforms like Pokemon?

What happens with a game like Baldurs gate 3 that had problem coming to Xbox S - and isn't on the Nintendo switch?

Also lets discuss what "released on all platforms, " means.

Is steam a platform? Epic? linux? Mac OS?  EA, or Ubisoft Launcher? Are you including mobile like IOS and Android?

How old a platform? PS4? Xbox 360? The 3ds?

If a platform (like say the Xbox one) refuses to release in Japan.. does Japan still have to release games for it?

It's not Sony's fault that Nintendo keeps persisting with an obsolete Tegra X1 chipset with 4gb's of RAM. It is not Sony's fault that people don't buy Xbox games cos of Gamepass and MS launched a next gen console that has 8gb's of RAM, a RAM count which can be found in tablets that elderly people use. Have you considered that Square wants to be third party exclusive to Sony because the competitors hardware is so bottlenecked that they felt they couldn't make a good game if they released it on there?

Same situation with the PS1. Sony didn't moneyhat exclusivity away from Nintendo 64. It's just that the storage space on the N64 was so limited they didn't want to be so restricted with how they developed their games. A worse game equals worse sales

all 3 points are arguable if you ask me.
1. it also costs more to finance the game, which may go beyond the scope that a dev is willing to finance a game for.
2. there's no telling whether hardware features would actually be impacted.
3. the 3rd party investment doesn't necessarily mean in goes into 1st party development., and even if it did that depends entirely on whether more 1st party games can actually be made beyond what has been scoped out.

If Sony, Microsoft or Nintendo don't fund some of these third party and indie games, they may not actually be made. The cost of making games is shooting through the roof and if they are given money to develop and help advertise the game it helps the game get released.

Azz is just mad Xbox not getting them anymore and Sony and Nintendo are successful are securing exclusives to sell hardware. Blame Phil. Bayonetta series dies without Nintendo. Astral Chain never gets made. Not everyone can just happen when you have 2-3 platforms to support. May not exist without them.

This assumes the developer has the funds to actually support all 3 consoles. Most don't.

This also assumes that these 3rd party developers/publishers are actually competent to do their marketing on their own.
Square Enix paid out big with it's AA output on Switch when they made them exclusive and published by Nintendo, which also handled the marketing rights.

Octopath Traveler, Triangle Strategy and Live A Live Remake have been success for such reason and Nintendo insistence to market these games to their audience.

Then Square thought they could get the same success by marketing the sequel themselves in a busy, but it was apparent they barely were able to market these games right. Octopath Traveler 2, despite being an all-timer and multiple other AA games from SE received almost next to no marketing from them which inevitably lead to lower performances.

Also, there's the fact a multitude of those 3rd party games would not exist or be founded if not for publisher deals, Bayonetta 2/3, Astral Chain comes to mind on the Switch. There's prolly a few of those as well on the PS5 too.

Nintendo of America also cares about Dragon Quest more than Square Enix USA does.

For what's it worth, they're becoming more and more rare anyway.

These games cost so much that 3rd parties by and large can't really play favorites with platforms nearly as much.

Street Fighter V was console exclusive, Street Fighter VI? lol, Capcom went running for the hills.

It's going to be difficult to secure 3rd party exclusives for any platform holder going forward when even platform holders like Sony/Microsoft don't want to lock their own games into their own ecosystems (lol). Like you have to be stupid or Square to still want in on the console exclusive boat. 

Sony paid big bucks for third party exclusivity during the PS1 era, it's just that the official messaging of third parties was about technological reasons because they didn't want to be viewed as whores. 20 years later a former Squaresoft exec openly admitted that they got the best deal among all third parties from Sony, so there's a clear implication that it wasn't only Squaresoft that got paid off.

Today's Square-Enix isn't any different. They still want to spend big on development for new Final Fantasy games despite their inability to make the series sell more, so they gladly take Sony's money once again.

On topic: When I read a topic title like this thread here has, I wonder how many gamers still haven't understood that the industry and gaming aren't synonymous. What's good for the industry is commonly not good for gamers or gaming as a whole.

In cases like the recent Final Fantasy games, it's certainly preferable for Square-Enix (the industry) to be exclusive to PS, because the financial viability of a FF multiplat is otherwise uncertain.