Windows has Windows Forms, WPF, and UWP; macOS has Cocoa; and Linux has … well, a lot of things, each with their own quirks, and not all of them with bindings into every language a developer might want to use.
This is a value judgement, ripe for disagreement.
Why do you think learning a new programming language is not difficult, as others perceive?
However, if you resent being forced to learn a new language, or if you are more of a copy/paste developer than someone who really understands what you're doing[0], yeah, a new language can be a very challenging barrier.
[0] I want to be clear: most people start out with very little clue what they're doing in programming. That isn't meant as a disparaging description. I wrote (and copy/pasted) a hell of a lot of code before I started understanding the underlying mechanics of it all, and I'm still baffled by a lot of the development world (again, hi Prolog and Haskell).
I'm not sure that's the primary reason for people to disagree. A larger reason is that a smaller language has a smaller ecosystem, and solutions in a common language need to be completely rewritten to the new language.