Why does this happen? You should only get a matchmaking penalty if you press leave game or close the application. If you can't penalize people who close application without penalizing those whose game crashed or disconnected, then its better to not punish the leavers than to punish the innocent.
Getting an Arena matchmaking penalty for game crashing or disconnecting.
One can see the logic in why this was done. If you were not punished due to the game crashing or a network connection, people would exploit that by deliberately pressing Alt-F4 (on PC) or killing their network connection to get out of an Arena match they were bored with.
But you have a point! It does punish those that suffer crashes through no fault of their own. The solution seems simple (at least on the surface). When you fire the game up again, you should be offered the option to "Rejoin previous session". This feature is already there. If you DO rejoin your previous session, there should be no penalty.
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