I don't know what the job mobility statistics are, but remember that the US workforce is about one hundred and fifty million people and the European one is a similar order of magnitude. You need to scale comparisons accordingly (eg comparing the US to Canada where the latter has a workforce under 20 million).
Additionally it is far easier to move in the US. There are no immigration requirements, language barriers, major cultural differences, different education systems, certifications (sometimes states differ) or similar impediments. Many states are "at will" meaning that employment is not protected to the degree it is in many other countries. This means that mobility can happen from both employee and employer sides.
I don't think job hopping is due to being self centred (in the pejorative sense). The US tends to be very productive which means employment and employees are more able to move around to meet needs. That they do so is not a bad thing.
I've known couples where one works a big boring established company in order to bring in the healthcare while the other works at startups. They would both prefer to work at startups but by the time people approach 40 there is likely to be some health issues forecast if not already happening. (Even the fittest people wear out body parts!)
And if anything economic policies have been discouraging mobility. Higher house/ing prices makes people sticky and diverts income into unproductive use, but seems to be a goal. (We'd all be better off with a lot cheaper housing costs.) The lack of competition in communications (largely due to regulatory capture) means that remote participation is a lot less effective than it could be. And of course health care is dysfunctional and expensive, although the care received by some of the people some of the time is world leading.