Or it's access to development tools required for making things for iPhones and iPads, and MacOS is just a side effect of that choice, and not a factor in the decision.

It's not. The reasoning behind the popularity of MacOS is very well understood: marketing.

What amazes me is that people who pride themselves on being smart when faced with Apple always resort to the laziest and most stupid of explanations for Apple's popularity: "marketing".

While marketing does play a bog role, it is still rooted in the reality: Apple makes good products (that are often leagues better than the competition in several areas), and as a whole the experience of using Apple products is better for a significant number of people.

What amazes me is that Mac fanatics never have any factual argument as to why it would be better than Windows.

All I hear are attributes that are supposed to be better (spoiler, they're not), but always without a single concrete example.

> What amazes me is that Mac fanatics never have any factual argument

First, stop calling people fanatics. And then, and only then, you will hear all the factual arguments.

If it were marketing, then I could leave MacOS for Windows or Linux. I cannot (without making my work harder for no net gain).