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.
Have you actually met or heard about any real-life long-term profitable sports-bettors, or do you just believe they exist?
If the story is real, the very fact they they had chosen to take their capital and invest it somewhere else would indicate that they themselves didn't have much faith in their betting skills working long-term.
Sports bettors who can make money on sports betting exist and probably continue to gamble today. And I also believe that they are investing it elsewhere because they think that nothing lasts forever and they have to have a business to keep making money even though they are still betting on sports.
If they invest the money from their winning bets elsewhere, it doesn't mean he doesn't believe in his skills but it shows that he can be wise and know when it's time for him to stop betting. People who can make money from gambling in the long term have more experience and a high degree of skill so they can see things from different angles and decide what is best for them.