Look at how you treat girls you don't like. Now look at how you treat girls you do like. Think about that for a second. Now treat girls you like the same as the ones you don't like and you will be surprised at the results. Quickest and easiest way i can tell you why this happens.
girls like guys who dont care , they crave attention and validation and when you dont try and look your best they will want you to like them so bad, and once you do they will not car anymore , the right way to get girls is to not care and approach them in a way that keeps them craving that validation from you and not get bored so they dont reject you