I am not aware of these kind of betting were available on gambling sites,only had these kind of bets with my friends and that's only just for fun.This kind of gambling can be highly predictable then how those sites were surviving while having this?
There are bettors so it's up to them on how they survive. They are not focusing on this kind of betting but it's just an additional option for their customers to bet on.
I think it's sustainable on their side providing some other interesting events that they can bet on like politics.
On the contrary, betting on politics is the most unpredictable kind of game. I am sure you have no idea what betting on politics could be like, if you did, you would understand better. I hate to bet on politics because I know the nature of the game, it can be deceitful and as well confusing and coupled with the fact it doesn't come very often like other games makes it even more discouraging.
IMO it's easier to bet on politics than an NBA game.
Especially if that is president election. We know who is win in president election when a lot of people talk to him. From your username i know maybe we're from same country and last president election really can be predictable.