I guess not just esports but as a game ect. Is the game growing in general?
It's reaching the heights of CS which is inevitably gonna lead to a roadblock
Before that point, growing viewership meant attracting existing esports viewers to your game's competitive scene--but there's ultimately a limited amount of esports viewers.
It's now more a matter of growing esports viewership as a whole rather than attracting viewers from other esports
and riot is already trying to do that by promoting the esports scene within the game itself via skins, the esports hub, twitch drops, etc.
tl;dr riot have taken hold of a sizeable enough slice of the esports pie, and now they have to focus on making that pie bigger