You need a license to operate in Spain. The license is fairly available (EU regulations enforce this). So, Polymarket is able to obtain a license if they wish to operate in Spain, if they follow the fair rules to obtain a license. Don't want to obtain a license? Don't want to follow the rules in Spain? No problem, but no business in Spain. Websites blocking works like that, too. Which makes sense: local law > remote law. Else I could host some websites selling LSD to Americans on the clearnet. No US government would accept that, zero chance.

Other countries such as USA work in a similar manner. Work permits such as green card, to name an example.

The people who complain about regulations and law either don't understand why they exist or how they work, or they have an interest in the abolishment of it because they benefit from that.

Then you get that BS about how USA is better off than EU. Well, if you're healthy, educated, and employed, sure. Otherwise? You can just use your eyes. Go drive through a rich and poor neighborhood in both. The poverty in USA is horrendous, and the effects are shown. We got poverty too, but not as severe. No need to go to that area between West and East coast. You can experience this right near the Bay Area. San Jose is supposedly a mess. I'd love to compare my visit to a Fry's in San Jose 2005 with today's.