Not only with sportsgambling but to all gambling games. Reason? Winning is never certain therefore playing more often would expose you to higher risk.
To me the main reason is that the casino are setting the odds that are favouring them more far more than the gambler. People go for the house in a way that it is an house edge. That is why gamblers lose more than they win.
Some gamblers may make profit if they do not gamble too much at a stretch and not gambling frequently. But some people continue to gamble and have fun and risk more and lose more.