I thought that they, whoever they are, standardized on 8x10 because in the olden days pros shot 8x10 and 4x5, and after pros stopped shooting 8x10 and 4x5, they, whoever they are, didn't change the standard, and so now nothing fits 8x10 without cropping, except maybe 6x7 which I learned today is really 56x67-68. Who knows why they picked 5x7 and 11x14 as standards. Nothing fits them, except 5x7 and 11x14 film I guess.
I found out the standard was screwed up about fifty years ago when I was shooting 35mm, and I had to crop my photos to fit the darkroom multi-easel, pre-cut mats, and pre-made frames, and that seemed really stupid. I was working in student darkrooms and one of the first darkroom accessories I actually bought for myself was an 8x10 "full frame" Speed EZ-EL. I had to cut my own mats. Then for a while I mostly shot slides so I didn't have to crop, except that the projection screens were square and so your slides ended up being letterboxed. When I wanted a print from a slide, I printed them myself full frame on Cibachrome. Now I just print full frame in whatever aspect ratio the film or digital format is and cut my own mats and use those metal frames which you can make any size you want.
Next time I go to the doctor I'll look through a bunch of magazines. I bet I won't find a single ad that is in a 8x10 aspect ratio. I never did any professional advertising photography, but always thought that the advertisers told the photographer what size they wanted, or photographers just left room all the way around the image so the advertisers could crop it any way they wanted. Of course, all that may be my imagination.