My feet got bigger for several reasons:
1) They became wider. My toes now are visibly separated when before they used to be squished together. Having toes separated is normal. Squished together is a result of wearing shoes too narrow, much like the result of Chinese footbinding, only less severe.
2) They became longer. Not a clue why.
3) They got thicker skin. Thicker skin takes up volume.
4) They got more muscular. Again more volume.
During the hike, as my feet became larger, it was apparent in my older shoes wearing out too quickly, in having my little toes on the edges feel like they were sticking out too far and being stubbed on things, and in finding myself having to wear thinner and thinner socks in order to be comfortable.
Numbers 3 and 4 subsided after a few months. Because I refuse to squish my feet into too small shoes anymore, numbers 1 and 2 remain.
I suppose if I had bound my feet into stiff boots, my feet would have done what feet always do when cramped, which is adapt by folding the toes under themselves or forming a bunion. I didn't want that to happen because it really hurts. Especially when you have a neuroma like I do.
So, to manage this, I wore shoes a couple sizes too big. To me it felt good. I used lightweight wool socks and that prevented slipping. The one time I used nylon liner socks, my feet slipped around too much and this caused me to tie my shoes too tight and then I injured my feet. Bruised them or something worse.
With lightweight wool socks, there was no slipping and I could loosen the laces all the way up to ensure there was no pressure whatsoever on my poor abused toes. My toes that have been abused by years of too small shoes.
With very wide, loose shoes, I'm sure my feet were encouraged to become enlarged, especially the enlargement described in number 1 above. But the alternative was blisters, deformed toenails and pain.