I'm not sure it failed.
I joined Mastodon in Apr 03, 2017 - but was never really very active because - well, there wasn't really much to be active with. It was ghost town. But it grew slowly and organically. Which was OK.
Then the big Twitter meltdown happened in Nov 22 and all of a sudden we got couple of million new users. There was a lot of adjustment, from new people and the old inhabitants. It wasn't very pretty (the whole CW debacle).
Many of those millions left and (presumably) went back to Twitter. But many stayed. The twitter InfoSec community is (mostly) on Mastodon now. Quite a lot of science-twitter is as well. We're far bigger place now than we were before 22.
Twitter didn't crash and burn (yet). People went back. But I don't think the migration failed. Some stayed and we're richer place for it.
But I agree with lot of the things in the post. Dealing with federation, quirky UI's, prototype services (hi kbin!) and other linuxesque peculiarities isn't what mainstream is looking for. The whole "just spin up your own fedi-server" might not be very sustainable/environmentally friendly compared to centralized well maintained datacenter. There are lot of problems to solve before fediverse is "mainstream ready".
But to be quite honest. I'm not sure it needs to be. Yes, I get that it's hard to "build following" without mainstream, but to be honest, I actually prefer more signal and less noise. And lot of the "mainstream" is just noise who follow popular accounts because they're popular.
teolan
beepnoise
roofuskit
ganksy