The difference is that a monarchy usually rules over everything and has the last say.

Steam is a monopoly only because every competitor has tried but failed to make a new compelling service.

Steam does have the last say within their platform (usually it’s the correct say), but they don’t disallow competition by lobbying or with other anti-competitive practices.

Some company just has to make a better service.

It’s not impossible, just no one wants to do it because they can’t make bajillions like they usually do in their other sectors where they can freely abuse the customer because there isn’t someone like Steam looking out for them.

So I agree with you, but someone must make a better service before the pc gaming marketplace marketshare can be more evenly distributed, but no one will or has. But keep in mind that Steam isn’t doing anything illegal and by no means should they forcefully be separated or anything by the government (they are not an illegal monopoly like google for example, they are simply a monopoly because they make the best service and no one is competing).