This really doesn't make sense. How many people have seen that an event has started and then decided to play acouple games only to realize that they got nothing from them due to not clicking the start even button in quests? Why is this even a thing? Just make it start automatically.
I've heard the argument that Riot does this because "some people don't want rewards and such from events". You are never forced to use anything you get from events or display any icons you got. If you don't want the stuff then just don't use it. Now if for some reason this is still not okay for some people, then why not add an option for people to opt out of event rewards, tokens etc? It is obvious that people who don't want these things are the minority in this community. Why make something unnecessary and just annoying for the majority of players?
This just makes sense.