what are the league champions goals in joining league of legends?

The thing is when we look into lore of every single champion it gives us their origin and their backstory behind their motivations or mysteries but never why they joined league and what league itself does for them. Is it a tournament for their goal to come true or is it harsh imprisonment like gladiatorshipesque fight to the death for the amusement of the crowds and the summoners choose (bet) wisely depending on the enemy's champion.If it were the first one then can we have like some kind of special cutscene or complete lore for people who earned lvl 7 mastery on those champions i know it would be revealed in like the first 2 weeks of the release on youtube or some kind of platform but it would be cool to get something more from mastering a champion and gives us a feeling of understanding of their respective roles in the bigger picture of lol. Anyways in the end im only sitting and writing this so Thanx for reading this :D