>>42273923
I think the reason Rainbow Dash moved to Ponyville because she wanted to stay close to Fluttershy.

Think about it. Flutters special talent is taking care of animals so of course she would want to move to the surface. But if Dash's lifelong dream was to be a wonderbolt why would she ever leave Cloudsdale?

Obviously Dashie couldn't bear the thought of her Flutters having to fend for herself in a whole new city so she went with her so that she would have a friend close by <3