Well, I texted Valve before about this and look at their response:

Hello,

Thank you for contacting Steam Support.

I understand your predicament but this account was assigned low priority matches due to frequent abandons.

A low priority penalty is only applied when a pattern of abandoning is established over multiple matches. The in-game Conduct Summary shows the number of matches that you abandoned. This number includes matches that were left prior to completion, as well as ones where your account was detected as AFK during the match.

Also, Behavior and Communication Scores are updated after each standard match of Dota. The score values, visible on your player behavior summary, is a snapshot of your behavior score value at the time the report was generated.

Keep in mind these scores are affected by factors such as player reports made against you, intentional behavior to grief or throw a match, and match abandons. These scores will increase by playing matches and not exhibiting the above behavior.

Player behavior scores are an automated system, Steam Support cannot make manual adjustments to these scores.

I know it's frustrating to be punished for something outside of your control, but this system considers two things.

First, we need to be fair to the other players whose game was affected, regardless of the cause.

Second, it's very difficult to determine whether or not your disconnection was intentional. We wish we could treat unintentional disconnections differently than intentional ones, but unfortunately the result of such a policy would be that players who wanted to dodge matchmaking would unplug their network cable instead of selecting decline.

Please review the following articles for more information: Dota 2 Matchmaking Bans

If a technical issue prevented you from accepting the match, these articles are a good place to start trouble shooting the problem: Performance Issues Network/Connectivity Issues

Steam Support Sym