Could be any number of things, honestly.
Message boards overall have been dying for a while as people move to other channels.
Youtube is packed full of information, no need to post and wait to find out something.
Almost everything is consumed on a mobile device now, is this format ideal for mobile?
An honest to goodness rejection of Disney by a huge swath of people for whatever reason... politics, cost, experience...
And so on.
I have seen forums for things come and go, from Sports to hobbies to Halloween. Change in software. Overwhelming ads. Change in management. Aging of a core group of contributors. Politics, covid, vaccines, war... when half the people are treated like crap (either way), they eventually just leave. Any number of reasons.