Community service is always good to do, but doing it to get unbanned in a game is a bit ridiculous don't you think? Not to mention people act drastically different online than they do in person.
Just because they did community service in their local neighborhood doesn't really mean anything to Riot or other players. Especially if that person is known for being extremely toxic in an online, anonymous atmosphere.
I get the idea you're trying to put out here; allow people to show positive examples of reforming their behavior through traceable means. But, Riot already gives players that chance even after a player receives their first warning/punishment. It's why we have a 4-tier punishment system. A player gets plenty of chances to show better behavior and to change, so by playing a lot of games and remaining positive in every game (or at least just refrain from toxic behavior) they are essentially doing their "community service" to League.
Even then, players are still more than welcomed to continue creating new accounts. Barely anyone is in the Tyler1 status of ban, so if they want a "clean slate" or "another chance" they are certainly create a new account to show they've reformed.
Wouldn't be fair if players could just do any kind of community service (I've done some where there's literally nothing to do for 2 hours and it still counted...) and then get their account back. Wouldn't be much of a "teaching" moment for that player to realize that actions come with consequences.