I think gambling came in more in later waves. The first wave of popularity (mostly StarCraft, LoL and fighting games) tended more towards funding from sponsors, and not gambling ones (red bull, monster energy, gaming peripheral makers, the game devs themselves, mobile games).
I don’t know much about lol or fighting games but the starcraft pro scene exploded after a gambling/match fixing scandal back in 2010! The first wave absolutely had this problem
