It's not about Twitter's ability to ban users it's about enabling them avoid a substantial expansion of their moderation responsibilities. Twitter considers it

It's not about Twitter's ability to ban users it's about enabling them avoid a substantial expansion of their moderation responsibilities. Twitter considers it a positive thing to have transparent and relatively equitably-applied rules, and this is an obvious positive for its users, and society in general (given how central Twitter has become to national discourse). Capricious one-off expansions that are difficult to justify generally (or that would require massive increases in moderation that pretty much everyone would hate) are the last thing Twitter wants.