Why Jungle? Forest? It's as big as a P a r k f u c k i n g p a r k g o e r c a m p i n g m y l a n e
"gg trash woodsman"
So does that mean junglers are Forest Dwellers? 
Feel free to call them Foresters then [sg-kiko]
A jungle is a forest, specifically a rain forest. Forest is the master type. The qualifier of a jungle just says that most of the trees aren't deciduous, meaning they drop their leaves all year around rather than all at once at like the fall.
Because bonobos live in the jungle and even if I am not seeing one every game, I am seeing this majestic creature in its natural habitat from time to time.
Because "jungle" rolls off the tongue better than "forest".
EDIT: Also, since junglers are always on their own, clearing camps who may kill them, and may even be dueling other junglers with no immediate help in sight (this is from the perspective of the early LoL days when junglers were farm oriented and had no defined jungle routines, and team also had no map awareness to help the players who decided to roam the jungle instead of running in the lanes; teams still don't have that awareness). People associate it with "the jungle rules" and thus the woodland on the map was called "jungle" by the early adopters of LoL.
Because a jungle is a forest filled with a wide variety of exotic creatures, both plants and animals.
I'd say between Blast cones, Pollen Plants, Honeyfruit, Krugs, Wolves, Raptors, Cinderhulk, Golem, Gromp, Scuttle, various dragons and a gigantic void beast, there's enough variety to qualify.
EHH doesn't have the forester or woodzerrer doesn't have the same ring to it like jungler
Some LOL regions actually call it forest.
In Russian people actually call it "forest".
It's woods