There are a lot of movies, Disney and otherwise, that have elements that might go over the head of young kids, but can still be entertaining to them. Zootopia has some pretty grown up concepts built into it, but it's not necessary to understand them in order to enjoy the fox and bunny detective story portion. Finding Nemo has a character die in the opening minutes, but kids can see it. The Wicked Queen in Snow White and the Seven Dwarves literally had kids wetting themselves in the late 1930s, and that's probably happened more than a few times since then. It's not like Disney movies are generally free of scary or emotional moments. Of course, what if you would like to keep your kids from seeing the "outdated cultural depictions" in those films? Maybe there was a feeling that the sequence is more intense when it looks more real? This could help explain why the animated versions of Lady & the Tramp and Dumbo are available while the live-action remakes are not. Is Lightning McQueen getting in a serious wreck significantly worse than watching Mufasa fall to his death in The Lion King? Of course, you can only see that in the animated version, as the remake is not available in the Kids Profile.
But are they more violent than the X-Men animated series from the '90s, which is available? Both Atlantis: The Lost Empire and Treasure Planet, are some of the most action-focused, and therefore violent, animated Disney movies ever made, and that might not be something you want your toddler watching, which is totally fair. Now, it's certainly true that regardless of ratings, many of these missing movies have things in them that might not necessarily be acceptable for all audiences. The Princess Diaries movies are both rated G, and both of them are off-limits.
Meanwhile, both Frozen and Frozen II received PG ratings, and both are available to watch using a Kids Profile. All three Cars movies were rated G by the MPAA. It would be simple to think this is a simple issue of ratings, but that isn't the case.