Idk about significantly less. Based on some research I've done, they make less, but nothing that I can't live comfortably with. Also just because something is in demand doesn't mean that I enjoy doing it still.
You are competing with both engineers and the MBA pool for the same job. The number of PMs roles available are a fraction of the number of engineering opportunities. The good APM roles at top companies are saturated with applicants and the average ones pay a fraction of what software engineering pays.