This only might work on maps , which has traps, can be used twice or three times.
We have many short maps, and having 2 lifes, makes gamemode being too easy, that will break the gamemode, and that we dont want that to happen. As Redspike wrote, AFK "manager" will kill respawners instantly, that "kills" maps, which has that "feature". Blu/Hale has too much work to try kill all players , running between different traps, what will happens to minigames? If someone havent die and has 2 life. Please dont make gamemodes being too easy.
If you really want to try giving second life to all players, you can set up that on second deathrun server and watch how much players it get/lose.