I know quite a few smaller independent commission artists are afraid to leave Twitter because they make their living off commissions and they can't or don't want to try rebuilding an audience elsewhere. The advantage is discoverability by the masses, who, as you said, are glued to a social media of choice, or google. They don't want to rely on art sites as those lean disproportionately to other artists, not normies who'd buy their stuff, and other social medias require that risk of rebuilding your audiance if the masses aren't moving there too. They've just relied on that confluence of Twitter pulling in everyone for so long that they don't know how or if they can market out to people who may not have heard of them before, while still maintaining enough of an income to hang on until then.
TikTok's advantage over Twitter is they did a better job at algorithming, and got the kids on board. It's major disadvantage is that it's video focused, so it's not a good fit for people who prefer text or for 2D artists looking for or showing off their work(at least to my knowledge)
If it wasn't for the panic over a non-American-operated social media rising to prominance, I'd put it up as what will end up taking over the social media zeirgeist, but with things as they are, Twitter is gonna be running on inertia and I don't see a full replacement happening that'll pick up everyone up for the next few years.