I am a size 14. I want to look through what they have in my size. I want my size to be all together. I don't want to spend an hour wandering round 10 different areas looking for size 14 in every separate area.
Normal shops sort by colour because they have every size in every style, so you can choose the style you want, then go and find your size.
Charity shops only have one item in every style, so finding a style you like does not help. You need to find something by looking through what is available in your size
I just turn around and walk straight out, if I go into a charity shop nowadays and find this silly useless colour rail sorting. So all my money is going to the charity shops that DON'T do it