It can be difficult to understand the various countries’ laws and their practical application for employers, requiring country-by-country study.

The same policies that provide strong protections for employees against being terminated can serve as a barrier against those same employees being hired in the first place. Different countries have chosen different points in that regard. Netherlands is stronger than the US for employee protections, but not as strong as Germany. France offers even more protections for employees.

Employers can’t treat EU as a single country, because, well, it’s not. They have to understand the laws and usually incorporate in each country. (None of this is complaining that it ought to be some other way, but rather just observing why you don’t see typical non-giant companies offering “anywhere in EU remote” roles [and agreeing with your analogy to North America].)