Flagged as Leaver in ranked for brief disconnection

As the picture shows. I worked hard to ensure my team won this game. I had a small hiccup like 15 minutes in where my computer forced windows update. It only took a couple minutes for me to reconnect and finish winning the game just to find out I've been flagged as leaver and lost 20lp.

How is this even remotely fair?

Why is this system so strict that if you're not around for a minute you're flagged as leaver and you lose no matter what you do. Why should I have even tried that game, it's not like I was going to earn LP anyway since by that time the system already determined I trolled my teammates and left.