Well because of the higher cost. Also cartridges (you probably mean SD as "proprietary cartridges" ala nes/snes/n64 are a scam) don´t offer any advantages compared to BD aside of being smaller as nowadays Games are being installed to the HDD, which is faster than SD cards.

The price. That's about it. Solid state is the future or gaming consoles and PC. It just is. I had no idea what SSDs were until I looked them up and bought a passport from WD Elements. Even though cartridges are more expensive the console cost immediately goes down in terms of cost and size because there would be no blu-ray or optical disc drive nearly eliminating the moving parts in the console. Carts are ironically the future.

Not just even in terms of gaming but just the whole PC experience is a different one if you have an SSD over an old magnetic drive, in the same time it took me before to get into windows I can now be flying to a dungeon in WoW from a cold start, tis nuts and especially with how cheap SSDs are becoming, I always recommend them to any PC user asking about how to make their system faster for any tasks.

Funny thing is you never had to blow in them, or inside the console's cart tray. It didn't help the game to work at all. The game would have eventually worked, whether you'd blow or not.

A PS4 Bluray drive cost Sony $28 back in 2013. It's probably cheaper now. It is very low power, so it won't affect the rest of the system (power supply, cooling, etc). Since Sony and Microsoft both have a vested interest in Bluray, it makes sense for them to include a drive in their consoles.

Blurays cost less than $2 (probably closer to $1). A 64 GB flash cart costs about $3 (based on what I could find through Google). As a publisher, I would much rather have the extra $1 to $2 for every copy that I sell by using optical media.

Since all games install to the local HDD now anyway, there isn't a big difference between load times (and most games hide the load times during cut scenes).

And personally, since I buy most of my games digitally now, I don't really care either way.

PS4 Bluray Hardware Cost Source
http://press.ihs.com/press-release/design-supply-chain-media/sony-nears-breakeven-point-playstation-4-hardware-costs

A 32-64gb sd card/usbstickstill cost a lot more than a disc which is just pressed out of oil.
Its the same reason why we dont get manuals anymore. Todays gaming companies are cheap as fu**, they measure the cost of a game by the digital price where they make 100% profit. Even if it only would cost 5€ more than the disc version it still would be too much for them just like a manual is too much for them.

Because digital is cheaper and more superior in every way.

Yeah but ... I can put it in terms for you to understand!

Solid State drives

Magnetic Drive

Basically think of how much eating you can do with that big juicy SSD inside your PC! Every Polar Bears dream!

Ironically SSD's are almost always going to be smaller in capacity than standard HDD's but still I hope the joke wasn't damaged by this slight mistake of mine

Because internal storage with immensely increased speed and digital only titles will be the norm after discs and there's no sense in switching to a format that would be both costly to produce and need heavy modification as opposed to a disc that already holds up to 200GB, not to mention the tandem production/distribution with movies that still makes discs useful outside of gaming and causes production costs to sink further?
I believe that's why no one uses cartridges.

Simple, carts are significantly more expensive to produce.

Carts are superior, but storage capacity and price are the issue.