[KVFinn]

>lots of various services/games/survey-things prefer or require you to use twitter login instead of making you sign up with them directly and they use the API on their backend for various things.

That's all I mean. I don't use Twitter on ID on mobile apps and I don't think this is common at all in the US, but it's not uncommon for random gacha games to tie player ID by Twitter accounts in Japan. From what I can tell nobody is sure what the consequences of the change will be, like maybe auth only uses are fine. But since nobody knows, all the big games are playing it safe and telling everyone to move their player IDs away from Twitter.