I don't see lots of nonhumans talking about leg dysphoria, so here we go;
To me, my legs feel absolutely deformed. Sometimes I become aware of them when I walk or sit and it doesn't just feel dysphoric, it feels straight up wrong.
Y'know those analog horrors with creatures whose joints are too many or misshapen or at the wrong places? That's what this feels like.
I'm a hare, I'm known for the fact that my hind feet are giant and I can use them to leap across fields in seconds and outrun pretty much anyone. I'm also a canid, I'm supposed to have legs that allow me to run, chase and hunt, with claws at the ends. But guess what? I don't. And it's something that I will never be able to change. I will never reach the speed I'd be able to reach if I had the correct body. Not to mention having to run on 2 legs instead of 4 is already a pain (unless your theriotype has 2 legs). I can imagine therians with more than 4 legs like insectkins, bugkins, otherkins with many legs, etc feeling this too and I can imagine creatures without any legs perhaps dislike having them at all.
Of course, there are shoes I can wear to simulate the feeling of hooves or hare feet, but they are still not mine. Leg warmers can look nice, but they don't change the shape of my legs. I can get into quadrobics for the way I feel about running, but that way I'm even slower than on two legs and all they do is look awkward and bring me pain because they are longer than my arms. (Besides, not everyone can do quads for a multitude of reasons, just like not everyone can run, obviously.)
TDLR: At least to me personally, I hate my legs because they don't and will never look or function as those of my theriotypes and I don't have a way to change it. The feeling of them being deformed in a strange way makes general everyday life and walking/running feel uncomfortable. Creatures with more or less legs who feel dysphoric about it don't get enough recognition, in my opinion.