I don't understand. HBO buys fights, not promote fighters. That is the job of promoters. If there is such a clamoring to see Rigo/Ward/whomever it is, then these promoters can do a show independent of HBO/Showtime out of their own pocket. The boxing business is predicated on the network paying license fees, and the promoter isn't putting up their own money.
The reason why is because casual fans make up the majority market, they want bloodshed and knockouts. They dont understand the sweet science or the definition of boxing "to hit and not get hit"
but you can be a slick boxer, entertaining and be draws (ie Pep, Leonard, Whitaker, etc). Rigo and Ward can't draw, and shouldn't expect any tv network to pay them big $$
