Laziness. Some sites are just blocking all European visitors on the mistaken assumption that that complies with GDPR. They're not willing to undertake any further dev work.
I don't think it's useful to use laziness to describe this, as it's needlessly perjorative. It may be that they've decided that the ROI is not there for complying with GDPR, or that the risk of an inadvertant fail is too high and expensive. Laziness may be the case, but it's unwise to assume.
If the site is the only business they have in Europe, it ought to be GDPR compliant. They’re essentially just pulling out of Europe rather than changing their product. It’s not like GDPR says every website on the internet is forced to serve the European market.
You say laziness, I say censorship. Which one of us is right?