Because when 1 or 2 people die in the middle of a team fight, that 20 sec run back becomes zero. There have been many clutch fights where if I had no teleporter the team fight would of been lost. Obviously this doesn't happen all the time but her teleporter on attack payload isn't useless, the problem is setting up on attack.How so, there is barely anything to gain from better respawn on payload
(also sneaking in a teleporter ambush is good too)