Bodybuilders in general do not make a lot of money to begin with unless you are one of the top pros with endorsement deals and sponsorship. Imagine how the women must feel. They work just as hard (if not harder) and only get about 10% of what the guys make.
Mr. Olympia 2015 = $650,000
Ms. Olympia 2015 = $60,000
Not a whole lot of money for women in this sport, not in the Olympia anyway. It seems to be fitness, figure and bikini (my favorite) competitors that get the most attention and endorsements.
Ms. Olympia seems to be the fringe division in a sport that is already on the fringes. No money to be made in sponsoring freakishly large women IMO.