Do they have official tournaments? This will make them more popular than tournaments conducted by random websites.
Many are conducting tournaments in Valorant, whether it's "official" or not. It can be done by a lot of gaming companies and even small time group of gamers, especially amidst this pandemic, which would make online tournaments be their only options. It is already hot on the gaming community and a lot of stucked-in-pandemic gamers are trying Valorant and enjoying it, hence no wonder it was already popular the day it was released.
In my own opinion, Valorant wouldn't be adopted that early by gambling platforms. Even Fortnite nor Apex Legends had limited to none betting activites, yet only famous in tournaments and streaming platforms. I guess the reason why it is rare to have bets in such games is that they are just rip-offs of the famous CSGO. If they would have a feature that would be unique in their game, they might have a chance to be addicted by most of people.