a) companies hiring only employees - usually only hiring in a set list of countries, because direct employees in places you have no presence are a pain. Hiring contractors puts the burden of a lot of that on the worker, so companies are more flexible.
b) companies hiring only in specific timezones - usually with the expectation that an entire team has basically the same business hours. But e.g. an US company with such a rule might very well take contractors from South American countries too, or an EU one from Africa). Without knowing further where exactly you are, that might be worth looking for as a signal (and if they mention time zones and you aren't quite in it, explicitly mention that you understand the requirement and are able to adjust appropriately when applying. Fundamentally these companies usually do not care that you actually live in those places, but they do expect you to match their work times)
I hadn't considered timezones as a limitation so that gives me some food for thought. I'm in an awkward timezone in NZ but I could make it work with a US company (have done so in the past). I may also try to float the point that I would be good to have around during out-of-office-hours as a potential plus.
There are always barriers to hire in different countries, because you cannot do business in them, or Labour laws are very strict and require an entity right away, etc. etc. There are companies like https://remote.com/ that help hiring people around the globe.
So there are remote companies that hire around the globe, keep looking and good luck :)
I get the impression that most companies hire up to their limit in foreign employees. The limitation isn't just for dev though. Keep in mind that they might also be hiring a star HR and such. Some may be leaving a slot open for the next star.