It depends heavily on the season. Bets go after the money, and the professional sport is organized in the way, in which different sports take turns, so they don't have to share the fan base.
Oh, I did not know that. I think it affects somehow. hence, the popular sports are held at different times?
As far as I know, they don't hold any major biathlon events during summer, at least in the northern hemisphere. I think, when a sport gets enough attention, its events are held more often, off-season too.