A free service probably isn't going to get sued into compliance if you accept sign ups from EU, but if you accept payment from EU that definitely counts as 'doing business' and you should expect to comply with local regulations.
Extradition would be quite reasonable if you were conducting a very large business, and/or ignoring significant laws, e.g. prohibition on human trafficking. But they aren't going to extradite you for failing to be GDPR compliant on $10 of app sales.
They'd have no repercussions except to block my site - and I'm guessing they didn't intend GDPR to turn into an internet filter.