Overall, they are different due to Evolution. They are all finches, yes. However, they are all abviously vastely different. Over time, they have evolved to better survive in whatever environment they're in. Look at the beaks specifically! There are a wide variety of different shapes and sizes! This is because each beak is better suited to help the finches obtain different types of food for their location. One may be better for eating nuts from tree while another may be better suited for digging insects out of the ground!
