This has been a question I've pondered on in the past. Being a film with 13 whole sequels, you'd think there'd be a little less longneck and a little more of everyone else.

Plus, Littlefoot's character arc was more or less completed in the first film, and to an extent the first sequel.
But at the same time, I get it. Littlefoot is the de facto protag of the franchise, so it's natural that he gets the lion's share of the spotlight. Also, I don't think Littlefoot's case of Main Character Syndrome™ is anywhere near as obnoxious as certain other franchises. For example, Lilo and Stitch. In that particular franchise, it feels like the livelihood of basically every character orbits around Stitch like the sun. In the TV show, Stitch is more often than not the ONLY reason anything ever gets done, always being the hero and cleaning up almost every mess - when Lilo is ALSO a title protag, y'know.

It's not always the case, as episodes like Yaarp and Spike show other characters taking charge and being heroes, but 9 times out of 10 it's Stitch who fixes everything. Whereas in The Land Before Time, yes Littlefoot is the main character, but he shares the heroism about equally with his friends and even other characters like his grandpa. It feels a lot more equal to me as a result. Littlefoot isn't the center of the confounded universe, he's EQUALLY as capable as his friends are - while still sticking out in enough ways to let you know that he's still the central protag.
That said, I think if we got more movies past the 14th one, I think we could've gotten more movies that bring focus to characters besides the big L. For example XII was much, much more focused on Petrie and to an extent Cera than on Littlefoot, and VIII was a time to shine for Spike and Ducky. In general the movies that are more focused on the non-LF members of the Gang have always stood out to me for giving them the time in the sun they hadn't really gotten before at that point. And that, I think, is part of why The Land Before Time as a franchise still holds up years later.
