In my headcanon, pegasus families are not very close, especially in Fluttershy's case. Her parents saw her as a disgrace because she could hardly fly. That's why, when she fell from Cloudsdale during the race, nopony ever came looking for her. She settled into a small cottage with her new animal friends and for a long time she let herself rot there. She felt alone, unwanted, and although she had her critters, she was very scared. It was only when Rarity happened to find her one morning, out looking for gems, that Fluttershy made her first pony friend since she lost Rainbow Dash.
Rarity grew up in a very liberal family, and she always found them extremely crude and obnoxious. She dealt with it as a filly, turning her attention more towards fashion and the arts. When Sweetie Belle was born, the Belle family fell into a financial crisis, and by that time Rarity was old enough to sell some of her designs. S