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?
Yeah I’m that case nothing can be done but say your site had a European operation that would be be covered under GDPR and the US parent would likely pay the fine to continue their operations on the continent