Technology

Although insta has been making inroads, it was the default in Japan for a long time for govt info, shop notifications (bars, art galleries, you name it), as well as other customer interaction.

To use community notes

1. Non-Westerner that never have or realized alternative platform exist.
2. Artist that dependant on mainstream social media reach. (some artists already have 100K+ followers there, fedi also have limited reach due to instance blocking, e.g. you're on Mastodon.art and want to reach Japanese audience (mainly misskey.io, but t was defederated on most of Western instance.)
3. People with social network bubble outside Westernsphere, they only have exclusively local feed on their Twitter.
4. People outside Westernsphere that already tried fediverse, but moving back as fediverse is still Western-centric or does not have their own community on feidverse.
5. Community that does not have monetary power to invest on their own fedi instance.

Inertia, at least in some cases. It takes a lot of work to rebuild your audience. Leaving is accelerating, though, albeit slowly.

Some people continue to gaslight themselves into thinking there is something to be gained from the audience they once had

It's becoming like Facebook, which is were people's parents, uncles and aunts and even grandparents (as well as technically inept organisations) are, but you yourself either moved on or are too young to have ever wanted to be there ("because nobody my age is there"), only whilst Facebook is merelly a Propaganda outlet for the Far Right, Twitter is openly Nazi.