Why do people shave their Pubic Hair

[Master Oblivious]

It is there for a reason right? Why we want to cut it off? If it needed to be off it would fall off.

Yes. There was a reason we were once covered with hair. 
As you can see with mostly Asians and native Americans, a process of evolution
has eliminated a need for most of their body hair. All hair serves a purpose until it
doesn't, them it's let go. Bush hair is protective but doesn't seem to serve a purpose
since panties and outer layers have been fabricated. Some stuff does just "fall off/out"

i.e. wisdom teeth. 

Nothing like a hit hot nasty bush that hasn't been washed for days and smells like smegma though. 
Bushy beavers were a big hit back in the days. Maybe they'll make a comeback. So attractive. 
A good trim before an angry bush protrusion could be considered.
Just a matter of taste folks.
It's as simple as that. Really, it literally can't get
any easier to explain. We're not talking rocket/brain science here.