Because their cost of living is insane, the social safety net is shitty, labor protections nonexistent, and they don't get any holidays, among other factors
Labor protections are indeed less, but this is actually a good thing. Like with many free-market topics, "labor protections" are a very dangerous thing, because they are a policy that sounds extremely good to the voting public, but many economists can tell you it's actually bad. US just got lucky, that it tricked the public to vote against it.
And if you're employed, especially as a SWE, medical care is better in the US. If you're not ... EU >>> US.