Usenet used to be where it was at for conversation on the Internet. Then it moved. Getting people to go back to Usenet is probably going to be as hard as spinning up a Facebook competitor.
It is purely a matter of free public servers. Right now, the free public servers are almost all Fedverse. But they could just as easily be Usenet servers. If the free Fedverse servers close like free Usenet servers did, then Fedverse will also decline. But Usenet actually has some superior features that Fedverse lacks (e.g. automatic merging of groups), so if free Usenet servers pop back up, it would take off again.