Because being basic means that you aren't dope, means you follow trends blindly and you're not an individual. But then the word "Basic" means class anxiety and the fear of being basic is just as basic.
Because girls hate when guys refer to them as "random" in the basic sense. Most girls see the need to point out that they are different from the everyday random chic.
They force personalities that are not theirs to prove that they are weird, unique and different without realizing how random they have made being weird become, or how concerned they are about what others think of them. This is the very definition of basic (Class Anxiety).
Be yourself, love what you love, enjoy what you enjoy and do not bother disturbing yourself with what others think. Be yourself, whether simple, basic, or weird and stop punishing yourself.