Non-software engineering disciplines tend to involve professional licensing that doesn't necessarily carry over automatically to other countries.

In my experience, the good ones do.

Medical typically does

I'm sure this strongly depends on where. I don't really know the state of the world today, but very distinctly remember curves being destroyed in the late 90s early 00s by a flood of professional engineers and medical doctors fleeing former Soviet republics to the US and not having their licenses or even degrees recognized and having to go back to school. There was a time where the quality of students in Los Angeles community colleges was probably higher than an average Ivy League university because of this.

Not necessarily. You might need to get country specific additional training which can be either easy to get or .. well not.

You've already described the main roadblocks. I suppose that those industries have less in-demand vacancies comparing to software engineering, as well as companies are not offering so many positions with relocation support.

Who wants to move to Europe to make 2k a month doing electrical or mechanical engineering? Since working for a US based competitor is not feasible from Europe in these fields, the pay tends to suck.

I would assume the biggest roadblock is they actually build physical products