Look at it this way UFC pulled in 4 million domestic revenue from a card headlined by Demetrious Johnson. Which is probably the highest revenue they've ever generated for a single card headlined by Johnson.
Not all UFC cards are created equal, or are expected to get 500,000 buys, or are budgeted for 500,000 buys.
I'd rather watch Ronda fight than the guys in the smaller weight classes.
I'd much rather see Dodson, Uncle Creepy or Benevidaz as champion of that division. Like you, I also think Demetrious Johnson as champ is more the problem when it comes to drawing fans then the actual weight class. If 125 had a more charismatic champion people would probably appreciate the division more.