technical issues with 3d aside, to get any meaningful information about it fitting, you first have to have actually have meaningful information about the product! this means that you would need a full 3d model of each article of clothing for each size from every seller. furthermore, you need information about the material it's made of and most importantly, how it reacts to being washed which means information about how the clothing was constructed. with all that information, you might as well be the one making the clothing.
stores aren't going by the wayside just yet.