To give you another example:
It's like making an hive map with only hive material (no wall, just 100% hive secretion).
The map would be dark, in fact you can only light areas with shoulder lamp and flares.
There would be many hole everywhere in the map for Alien to came in and out the room.
Sure Alien might enjoy this slaughterhouse but Marine probably ain't be killed every 2 seconds without getting a chance.
It's almost the same thing for the jungle since you can't force player to do whatever you want they won't work in team and get their ass kicked everytime over and over again.
This is unbalanced and bad for mechanics.
I don't mean to remove the dense vegetation in jungle map be warned, just to put other elements where Predator and Alien may have disadvantage if they go in it.
Gameplay must be balance to work well, map also.