Hell Weidman beat Silva by KO and didn't get the kind of attention that Rousey has for beating the likes of Meisha Tate. I think there's a bit of sexism towards Ronda because of the way she looks. On the other side you have a very humble composed new champion in Holly Holm who has incredible work ethic and discipline. Maybe if she was this super hot chick she would get all the attention. She's 10-0 now and if Ronda can't take her down in the rematch we could be looking at a new dominant champion in the Womens bantamweight division.
The money and marketability comes from being able to grab the attention of the casual fan
Ronda grabbed it via her looks and persona, Connor McGregor with his mouth, Brock Lesnar with his WWE fame etc etc
The UFC can obviously recognise marketability in a fighter and do what they can to optimise it as it benefits them directly to do so (seeing as the fighters are all on central contracts signed to the company)
Same goes for other sports - Anna Kournikova being a prime example from tennis (although of course the marketing people are more third party I guess)
Unfortunately it's not just about ability and performance. Sure the hardcore fans of any sport will respect and appreciate that above and beyond any other factor but the causal wider market will be drawn in by hype and marketability created by looks, personality etc and there will always be marketing people who will seek to maximise that I think