I have a cousin-in-law who was married by a defrocked Catholic priest. It wouldn't surprise me if he acquired said priest through this service.
IMO the reason "why" there is a market for this is that you have "customers" who are heathen/pagan & want to stay that way, but they're superstitious enough to want a "real" priest to marry them, "just in case".
A "real" church priest/pastor probably wouldn't sanction such a marriage due to their (im)moral lifestyle, hence the market for Rent-A-Priest.
Would a "real" church sanction an annulment because they've gotten tons and tons of money in donations? ie, Kennedys?