"ban" twitter how? go to china and ask to license the great firewall? you could restrict it from operating a EU office or servers, you could restrict it from taking payment in euros, you could even restrict EU domiciled business from paying it but actually "banning" it is a much more authoritarian option.
who says you can't still advertise to them? if twitter goes the "screw the eu" route they don't even have to follow gdpr so that makes for a competitive advantage.
