I think Material UI is going pretty strong, too? They've just released a beta of version 5.
I think overall the comes-from-corporate-entity frameworks are probably still a better bet than the one-persons-pet-project ones - there are loads of those, too.
Material UI isn't coming from a corporation in the same way as the others though. Material UI is an open source implementation of Google's Material Design system, but it's not in use by Google AFAIK.
Take Zurb Foundation for example, as far as I can tell its basically become abandonware. Foundation 7 has been promised forever and yet we're still stuck with Foundation 6 which has all sorts of bugs and gotcha's that will catch people out because the framework is out-of-date in comparison with the technology that people are using to access websites.
The only exception to this is Twitter Bootstrap which has been consistently kept up to date. Whilst I don't agree with some of the design decisions in the latest Bootstrap 4, it remains a solid, well maintained framework.