Probably used some crappy house paint
This was comedy yesterday: https://youtu.be/Wz_JVFW83iY?t=554
It's not nearly the first time an absurb, stupid take on something gets played to extremes for laughs only for that the be the actual path taken despite all the warnings/math/science/reality that have to be ignored. It won't be the last, either.
Stream of consciousness:
The institutional users already had to have identity management in place. The PKI was already "there" so self hosting and falling back on the existing infrastructure was a pretty nice win.
To get really big as a social media site you have to monetize your users. If all the messages are encrypted in a decentralized manner then there's no way to monetize them. It also takes away some of the "social" parts of social media. It'd be fun to see what would happen if everyone spent a day posting nothing but ASCII armored messages to web-of-trust style keys to RDDT.
Open social media sites will always have problems with bad actors and people who just kind of wander in and make themselves at home.