Wages in Europe are shockingly low from the perspective of an American.

One example: The UK is a reasonably wealthy country. Median household income in the UK is 29,400 GBP (36,000 USD). The poorest state in the US (Mississippi) has a median household income around 43,000 USD

This applies doubly for high-paying jobs (devs in wealthy parts of the US make 2-4x+ what they would in wealthy parts of Europe).

I switched to working remotely for a US company a couple years ago, and while I used to have a "sure why not chat" policy with local headhunters I don't even bother anymore because the offers they can come up with are astonishingly low compared to my already-below-market-for-the-US wage.

That being said, at the low end of the job market (minimum wage or close to it) people can make more here than in the US, and with paid vacation and healthcare to boot, and there's less inequality as a whole, but the fact remains if you're trying to sell something there's less money to chase.

Sure, healthcare is no-cost, you get a month or more of vacation a year even if you're in low-paid work (if it's full time), and quality of life is better in many respects, but once you get away from the nordics, really, there's just a lot less money about.

Also, lack of a common language is still an issue (How many versions of komplett.no needed to be translated?), and not just for sites, but for support, logistics, etc.

If you send physical products Europe is expensive to ship in. I can send stuff to the US cheaper than some of Europe (though customs applies, of course)

I'm in Europe, and would like to start a company, and even I would be using my local market primarily for testing and then focus on the US. On the bright side, devs are a hell of a lot cheaper here.

Poland, Bulgaria, Romania, Greece have a lot of very smart and hard workers, but they are not (yet) wealthy countries. People in eastern Europe simply do not have the disposable income that Americans or western Europeans (usually) have.