Yes it does. If there actually was a bigger demand than there is supply, the salary would raise. The main reason why it doesn't is because a programming language or frameworks are not a barrier for any top developer. Skills usually transfer very well.

The real crux of the matter is that these companies don't want to pay top salaries and thus don't get top developers. As long as there are people who navigate themselves into such niches and are proud of it, the salary for these specialized jobs will stay where it is. Simple as that.