The aisles are pretty narrow on commercial jets. I would look at that.
Well for myself I don’t have trouble walking down aisles nor even buckling in seats, I am not particularly overweight for my basic size (although I am a bit overweight for it). But being that I am 275 pounds there are some things I am just too heavy to safely do that more regular sized people can. Some roller coasters that have the bars that come down over my shoulder won’t lock for example (and wouldn’t even if I were at my ideal weight probably). I don’t feel as comfortable on scaffolding as I would if I were lighter etc. We come in different weights and sizes and sometimes we can’t even diet to do anything about it, and sometimes it means there are jobs for which we are not well suited. Not the airline’s fault at all.