Leaver buster edits?

So recently I had afked in an Ascension game due to my power going out. I have been playing league for around two years and I have recently received a 20 minute leaver buster for the ascension afk. In the beginning of my league years I did not understand the functions of the game and afked in a ton of games. AFter the first few months, I stopped afking and leaving games. My question is why I (or anyone) should be forced to have a minute leaver buster for a random occurrence (I would understand if it were ranked). 20 minutes for leaving in a casual game simply does not make sense. Of course if it occurs a few games every week then yah, but if I afk in around 3-5 games in one year (ive spent ~1250 hours playing), then why should I have to wait 20 minutes instead of a lower time of 5 or 10 minutes.

Edit: I understand it starts at 5 then escalates from there, but don't you think some adjustments should be made (maybe have it reset off of positive behavior over 5-6 months).