Unfair mutes/bans

So this is just something random that I would like an answer to if there is one. Why is it that some people who get reported for verbal abuse or offensive language get muted or banned while other's don't? For example, my brother was extremely toxic at one point in time and got muted for 98 games. He completed those games and stopped being toxic. He would still say things like "please focus on cs" or "Please stop feeding top." The worst thing he has done recently was call someone a noob, which in my opinion, is not offensive at all. 5 minutes later he got muted for 16 games because he had called someone a noob and told them to learn from normal games before he played ranked. On the other hand I have a friend who verbally abuses anyone on his team who makes a mistake. He goes all out too. He even uses racial slurs and pretty much gets reported every other game he plays. What I don't understand is how he has never been muted, or banned. Can anyone explain to me why someone who fixed their attitude gets muted within 5 minutes of being reported for calling someone a noob but someone who's more toxic than acid has never had anything happen to them before?