Cost. Optical disks are orders of magnitude cheaper than solid state.

i can kaz hiria at e3 2015 saying:" it is the beginning of a new era last gen we brought to you blu ray and cell technology, this gen we bring you ultra cell technology it's 5 times more advanced, and a new disc! it can store 20 times more then a blu ray disc. 

we are going to have a 499 sku 750 gb for a ps4 without that laser technology its just bluray and a 999 sku for a ps4 with everything included and it comes with no controller and no game."

suddenly reggie comes and says:" i have an announcement i'm sorry but i messed up with the price of the wii it's actually 250$"

then a ms executive comes and says:" well i'm being nice here, i'm going to tell you a secret the xbox720 is at 400$!

then at the launch date of the ps4 sony announces it won't support it anymore and it officials gets out of the console buisness, but it anounces a new psp which comes with bluray capabilities.

hopefully that wont happen.

Tech lifecycles are becoming too short. Consumers will stop buying eventually.

Maybe but this gen has been one hell of a ride so far length wise. If this gen last ten years how long will the next one be? I don't think i'll live to see 10th gen videogames systems.

I am not talking about video games here.

Then there's this:

Blu-Ray are fine for now and next-gen. Today's are barely 50GBs, and if they need more space, just use 4 layers. If 100 GBs are still not enough for you, then you have a real problem with developing. Heck, by the time PS4 hits, one Bd will probably already have 100GBs.

I think it would a great mistake to use a different format for the PS4. With the PS2 CDs were already too small for big games, and recent PS3 games show that now DVD space is too less. But with Blu-Rays still having air to bigger sizes, PS4 should just use BD.

For PS5, maybe we need something that big. For PS4 all we need is the 33.3 Single layered Blu Ray. put a 12x drive on the thing and it'll read quadruple layered discs easily. Best and most cost effective solution for next generation.

i bet this is just another version of the hologram discs which already can hold 6TB.

http://en.wikipedia.org/wiki/Holographic_Versatile_Disc