Gambling on sports is one of the oldest types of gambling.
And, look. If you have the cash to spare, and gambling isnt a vice for you, it is kinda fun. Thats kinda the problem, its easy for the average person to get into it with some friends as a way to have more fun watching the game only for that to be the first domino.
Fantasy football is literally a 20 year plan to create a childhood gambling pipeline, which they finally pulled off with the recent rounds of regulatory capture.