Forget all the stuff out there that says the GDPR protects EU citizens. This is a question of jurisdiction and enforcement. Say I run a blog under a business registered in the US funded by advertisers in the US. A EU citizen that comments on posts issues a GDPR request that I ignore. Their government fines me. I tell them to get bent, I am out of their jurisdiction. What can they do at that point?
This is a good article on whether non-EU websites have to obey the GDPR. It boils down to two criteria:
or
The latter includes use of advertising cookies, location tracking, etc.
If neither of those apply, you can probably ignore the GDPR.