Why not allowing leaving on custom games?(1v1's specific)

On Custom games I don't think you should be forced to wait to for the game to end to leave and play for real. I mean you are not getting any ip or xp or anything for the game why are we not allowed to leave. I don't like this feature because when I 1v1 my level 30 friends I am level 18 :'( I get tired of dying and leave but then they just troll me by staying in the game and leaving their computer on so I can't play. Especially 1v1's "your team needs you" you are your team no one else on your team will get mad at you for leaving and you are giving the enemy a win so why? Another thing is if you are on the reconnect screen and the game ended it doesn't do anything you have to reconnect so the game recognizes that the game finished. Thank you for reading :/