Yeah, if you live in SV and want to make $120/hr on Upwork, go pound sand. But those salaries are pretty good for people who live in modest Midwestern towns or countries that are not America.
Some people have no idea how much it should cost so that's why you see complex sites with only a $500 budget. It's a smaller pool of better paying projects. You're not going to get SV rates but you could make a decent living from.
As for me one of the clients enjoyed working with me and we moved away from Upwork and just pays me directly now. Which I think is a common occurrence, and probably does reduce the amount of higher paying project. Once you find a good developer you tend to stick with them.