Keep in mind that if Twitter took a cut of tips, that would automatically trigger the App Store's 30% in-app payment tax for any user who tips on their iPhone. (According to App Store rules, if an in-app payment goes 100% to the creator with zero platform cut, then Apple foregoes the 30% fee.)

It's similar to why Clubhouse isn't currently taking a cut of creator payments: they can't do it without paying the App Store fees.