I think Jacob likes Bella so much because if toi are a boy and toi have a friend that's a girl toi will start to notice that toi have feelings for her. That's only if toi two have been Friends for a long time.
It's not really something which can be explained. People don't exactly choose to l’amour someone else. Some fans theorise that he was drawn to her because she was related to his future imprint though, similarly to how Sam dated Leah before imprinting on her cousin.
