Probably because you are tall with long legs.
shrug
I wouldn’t let it bother you.
It’s all in the rider and horse conformation. My TB is built pretty big, and he also has a llama neck and long legs, so he looks quite a bit taller than his actual not-quite 16.3hh. My WB is maybe 16.1hh, but takes up a huge amount of leg- we call him The Tube. People always think he’s massive until they stand next to him and realize he’s just a tank. A short one.
I have relatively long legs, so I look appropriate on tall and/or round horses. But, even though I am not even 5’5" and have a short torso, my legs make me look stupid on most ponies- I moved up to horses when I was 12.
My ISH photographs huge, people think or guess close to 17hh from pictures… he is actually a thin hair under 16hh.
I think it depends on the horse and their build. I have a 14.1hh mustang and I am 5’7" and I don’t look big on her, or my thick 14.3hh Paint mare. However some 15hh-15.2hh horses I have ridden I look large on. But even people here on COTH agreed I do not look too big on my 14.1hh mare.
