Brakes.
As Plow said, unless you feel comfortable without a front brake and dont feel the need to have one: take it off. Otherwise, don't. Not having a front brake sheds a bit of weight but thats not really why people take them off, the whole bike just feels and looks so much cleaner without one and theres less stuff to get in the way. And some riders really dont need one.
It is also a very fashionable thing, a sort of trend. Just like you, people will see nice street brakes without a front brake and do the same, with no second thought.