People see valorant tournament -> "Yo that character looks fucking sick" -> "Yo that player just did something Fucking epic wtf???" -> "I wanna play like them" -> Download valorant -> Riot makes money off of them playing and/or buying skins.
The potential of becoming an esports star keeps a community hooked on wanting to grind the game, therefore forcing them to play longer and stay on the game, which means they'll see more skins they like and spend more money on the game over time. All around, VCT makes Riot lots of money, which means riot wants to give the teams that bring them such numbers lots of money.
The esports teams benefit from sponsors, Content, and franchise money from riot. Not only giving riot attention but also giving the companies that own/partner with them attention. Take Nongshim for example, You see nongshim showing support to a game you care about, it makes you more willing to buy nongshim products, therefore nongshim makes money.
Most esports teams have a Business behind them in some way. The team acts as a billboard catered towards a younger audience.
The point of investing in esports is to advertise your brand to a younger audience who isn't interested in the newspaper, Television, or billboards anymore. It's expensive as fuck and kinda unstable, but when it works it works.