One reason could be that a network of well-connected right-wing influencers on TikTok share AfD content and help amplify it, according to Verwiebe. Another could be that the majority of AfD candidates, more than any other party, are themselves active on the platform.
I have another: It's in the financial interest of Tiktok to promote an extremist party with extreme neoliberal views in order to make more profit.
It's the chicken and egg problem. People don't move to Mastodon because there are less users and there are less users because people don't move.
However if someone consumes less social media because there are "less people making noise", I consider that a good thing.