That's why most of bettors always lose, even though many people say it's a skill based game, but it's still not enough to give a higher guarantee the gambler will win and beat the house.
As much as I agree that some types of games that are considered gambling are actually skill games (namely poker) I wouldn't say the same thing about sports betting. Sure, if you have good analytical skills and knowledge of the particular sport you could potentially spot opportunities when the odds are misplaced by bookies giving you the mathematical advantage, but that's more about finding anomalies. By design, sports betting is not far away from "classic" casino games where the house has the edge. That's why we don't see many (or at all?) professional sports bettors.
I agree,many people claim to be professional sport bettors by opening several accounts in tipping websites and other related channels in social media yet the fact is that they all lose in the long run simply because as you say it is hard to always hit a win in sport betting.Especially in tennis where they have the low odds of 1.15 and such,I once payed a premium subscription in a tipping service,not much just 9.99 GBP monthly and what these guys were doing was collecting such 1.15 odds from tennis,basketball and other sports,they almost never used soccer and making a parlay with odds of 2,I must admit the first month I ended in profit but several months after I ended up losing big amounts so I don't think anyone can win in the long term in sport betting.
i believe, there are few of these sportsbettors who can win in the long-term. but those sportsbettors somehow invested some of their winnings to businesses, so even if they go back to betting, they have other means to earn money, so they are not totally broke.