In my experience, legal and tax complexities are more than sufficient to restrict the countries that we have remote workers living in.

We work globally so practical things like timezones aren't really a factor; we have plenty of experience working around them. That even goes as far as things like personal security in locations that are particularly dangerous. In my line of work that usually means risk of kidnapping. It will be a factor we take into account but wouldn't usually be decisive.

Having said that, I have been involved in setting up multiple offices in new locations. But only where we're expecting to have a significant presence over the long term. Essentially, where we can amortise the costs of legal and tax expertise.

Source: reasonably senior executive at a very large, global financial organisation.

If you want to work remote, then easiest approach is to establish yourself as a company / self employed and do effectively freelancing. Entering into employment contract with somebody outside your legal presence is a problem for lawyers. Paying an invoice to a company somewhere in Eastern Europe is not a big deal.

yes, it's all of the above.