Back-building the history of the far-flung Apple Family reinforces Applejack's place in the main six as the most grounded pony in terms of personality and also her place in the world. She has not been given an ambition that drives her to be anywhere else or anybody different than who she is or has been since she was little. Parents at this point might be a pendulum swing too far to one side of the balance of characterizations in this show, at least until others get some time to accrue history.
Pinkie and Rarity are the ones closest to her in their ties to the community and family, and that's a distant second and third.
Pinkie is so flighty, and her kin have an absurd vocation of farming rocks. She's part of Ponyville, but it's a very singular role, not a family affair. (She does get to babysit soon, though.)
Rarity has parents we barely see, but at least she has a sister who figures more strongly in various plots. Interestingly, she's characterized as being in love with someday being somewhere else more exciting, and she's had quite a time making a splash this season.
The contrast is extremely stark with the pegasi, who have no parents or kin (edit: that are defined). At present, they barely have a home town. To top it off, Fluttershy's isolated home and reserved nature have her at the periphery, and outside her circle of friends she has few connections. It doesn't seem like she minds, but
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Rainbow is interesting in that like Rarity she (in season 1 at least) had plans to go somewhere else. The Discord episodes showed she had a stronger personal tie to Cloudsdale, but she doesn't live there or in Ponyville. I hope the future episode with her and reading gives her a bit more to do or a bit more to be.
Twilight is from elsewhere and has parents that live far away and had a brief non-speaking role. Her central role in most episodes has lead her to be have a secondary role as a thriving transplant. She indirectly has a leg up on Applejack because she's associated with Celestia. That's a root that trumps every other in terms of depth.
How fitting that Celestia's act in Granny Smith's history is a figurative and literal planting of a seed that was the germ for a series of events that would lead to the salvation of her sister generations hence.
I'm not sure I'd be the one to argue that she's that omniscient or machiavellian to have done so on purpose (others use the goddess pony concept more than I do), but it seems after 1000-(age of Ponyville) years, she had the karma of centuries of good deeds or had learned to be a badass even if she didn't have it all planned out to the most minute detail.
edit: made math more clear