There is an auto draw if two people disconnect within the first 2 minutes or so.
If someone disconnects or leaves, yes, the game becomes unbalanced and unfair, however, that is why we ban for leaving and we ban people for breaking rules. Recently there was a
suggestion regarding adjusting autoban to compromise its vulnerability making autoban bit harsher and effective. Check it out. A ruined game is ruined already, so maybe we should auto draw such games. But, as goat mentioned, people can also abuse this system and draw games in their favour. Wc3 is an old game and how we run our games and regulate them is the best compromising effort that ENT can provide imo.
!draw command is a "vote". You may call it unsportsmanship when someone refuses to draw and you may be right, but it is arguable. !draw is a vote, therefore, no one is obligated to agree.