There are multiple factors. Some H-1B are very skilled and in need. But there are consultancies who make money off these workers and don't care about the skill, they'll do whatever they can to make money. Also another factor is suppressing salaries as people need to compete these lowly paid workers...

H-1B's are a race to the bottom.

The point of H-1B is to lower wages. Not to stabilize them. It's a way to increase supply of labor which puts downward pressure on wages.