It was enforceable before too, thanks to the Data Protection Directive from 1995. GDPR is an harmonization of the various national transcriptions of the DPD, plus higher fines, a better cooperation mechanism, and data portability (which is a bit useless but it's nice to have). Cookie banners also predate GDPR (it was the ePrivacy directive).

> Yes, but now with gdpr it's enforceable, what if twit decides to stop providing that data?

Why would you want a law with high compliance costs to solve a problem that was already solved? It makes no sense to impose the costs unless the thing it purports to solve actually presents as a problem.