I don’t care what you “invest” in - anything CAN be a gamble.
Likewise - you can make smart choices to guarantee a likely profit on just about any investment - including gambling on sports.
It’s all about proper risk management and financial controls.
Stocks go down as well as up - historically though long term they gain as a whole. Likewise - big faves win regularly - but historically betting underdogs has been slightly more profitable.
Pick your spots - do your research and manage your money. If you’re good you will make a profit. 90% won’t because they didn’t manage it right - but they will keep throwing money in and think they are winning when they wind up with more than they started with.