I think Jacob likes Bella so much because if आप are a boy and आप have a friend that's a girl आप will start to notice that आप have feelings for her. That's only if आप two have been फ्रेंड्स for a long time.
It's not really something which can be explained. People don't exactly choose to प्यार someone else. Some प्रशंसकों 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.