Because the Vita was less popular everywhere outside of Japan, which makes that there are less units available and the units cost a few times the price of a psp second hand. (in The Netherlands the PSP is just under 100 Euro second hand, usually with 20+ game discs, a vita starts at 200 without any games and often without a charger)
A lot of people also still have a PSP just hanging around, less so with the vita.
A lot of what Proton-GE brings from my understanding is a larger support for Media Foundation, which can't be added to Proton itself because of license issues (Proton is from a commercial company, where Proton-GE is from an individual).
So aside from the stuff that has been implemented differently, running Proton instead of Proton GE is like trying to game on Windows N editions.
I played the F-Zero game recently in an Arcade nearby, it was amazing! I was so suprised when a buddy of mine went like: "Yeah, there is just a Gamecube in this".
It was very broken for a long time. Since fairly recently you have WiVRn (specifically wivrn-dashboard on Arch) for Oculus (more supported though) and I would daresay it works better then SteamVR used to do for me on Windows
There is a chance the led is also used as a important diode in the circuit, plainly removing it can greatly reduce the lifespan of the device. (more common in cheaper products)
Adding a appropiate diode in it's place is advised.
While I think this change is great, I am not directly convinced Safari should be included in the list by their own rules, considering the app has not been explicitly downloaded by at least 5,000 users in the prior calendar year.