Can people actually get punished after just straight leaving the game?

So basically i got into a game with my friends(on my alt not thhis once since its banned), and we were good for about 5 minutes. Thats where something normal started to happen, bot started feeding! Yaaaay. They lost against ahri adc and evelynn support, and they left. Me and my other 2 friends reported them and i expected an instant feedback as usual because i get one everytime i report somebody and they get punished. So i asked my other friends i they got an feedback about that and they said nope. So why do players get away with leaving the game just so they cannot que into another game for what 10-20 minutes, while every single other offence is punished by a ban? And even if they got punished without me getting the feedback why is the punishment for leaving higher que time instead of a ban?
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