Again, you want a indie announcement? Go to the PS blog and you'll get one almost every day or at least every week. Or just go to their Youtube channel, that thing is full of that shame. E3 is for the big guns, that you don't get to see every day and that's how Sony used it. Frankly I don't need Sony to put another indie game on stage at E3 after they put NMS front and center for two years just for the whole thing to turn into a huge fiasco or stuff like Rime (even though that was Gamescom) where the whole thing just turned out to be nothing but smoke and mirrors anyways.Also, Sony emphasized indie developers early-gen because back then, Microsoft still had very restrictive policies. The tactic was effective in that Sony one-upped MS on who is the more pro-consumer/pro-developer company and eventually, MS allowed self-publishing.
Sony likes and supports indies, that's all fine and dandy, but that doesn't mean they need to put these games, that don't expect to sell that much in the first place, in their E3 conferences where 95% of the people watching just consider them as nothing but filler for the bigger stuff, which leads to them being all but forgotten by the next day anyways. PSX is somewhat of a different story since it's more of a fan event but you don't put 8bit-2D-Sidescrolling-Shoot-em-up-Nr.238 in between God of War and Horizon Zero Dawn at an mainstream event like E3, that's just asking to be completely overlooked.
Now, showing off indie games on the big stage doesn't have as much of an impact as it used to. Everyone is doing it, so Sony needed to find a unique way to present games at E3 and unique, it was.