First and foremost, gambling is always depend on luck.
Gambling is definitely a game of luck. But here we are talking about sports betting. Sports betting can be considered as both game of luck and skill. As in sports betting you need to analyse the sports event, do calculations and then only bet in it. So if a bettor is losing, then it only proves that he doesn’t have required knowledge on that particular sport. To be honest, now for a few days I haven’t seen many gamblers losing money on sports betting, yes they bet on odds with less returns, but never seen losing more than winning.