The issue is that in order to block a website on the internet from a subset of users, there is a huge amount of work that has to be done to make it effective. I can't imagine twitter would bother with any of that, and why would they? It doesn't cost them anything to just shut down their EU offices/operations, stop complying with all EU laws they have to comply with in order to do business there, and make twitter (even more) American-centric. EU users can still use it if they want, since at the end of the day it's just a website on the internet.