[2019] Why punish people for leaving at hero selection?

If you’re in Quick Play and you leave during Assemble Heroes you’re not punished.

Would you be willing share how much of a concern leavers during both casual game modes and Competitive game modes are to you guys right now and if there are any plans to increase or modify the actions done to deter leavers in Overwatch?

I am in the middle of composing a topic about this (not ready yet) but while its on the subject here, I know the community would love to get an update on this.

I am not sure if he elaborated the full rules. There is an older post from former Community Manager Lylirra about that:

Source: https://us.battle.net/forums/en/overwatch/topic/20745234477#post-6

In addition, if you are not earning enough endorsements over time, you can decay your endorsement rating.

Well he did deliver the correct fact correctly, if it was during the Assemble Your Heroes phase, but not the Setup your Defenses/Prepare to Attack phase, leaving then has no impact. However, as I said, you can decay if you are not earning enough endorsements in your most recent games played (even if you receive endorsements in the most recent round completed).