Like food business must deal with the cold-chain, Clothes businesses have distinctive features other retail areas don't have, there's a reason fitting rooms exists in clothing brick & mortar stores.
How do you replicate the fitting room experience online? with colors you can see differently on a monitor, texture you can't feel, sizes for each body type that are different, etc. , the best way today is to order more and return.
> Why exactly is this unbelievably damaging to environment is an exercise left to the reader.
Well people need to find clothes that fits them. So they're either left with going to a brick & mortar store, or ordering online and returning items that don't fit.
Me and all other customers driving to the outlet malls (assuming that mall has all the stores we're interested in, otherwise drive to each store separately), and driving back in our cars is certainly more damaging to the environment than one extra shipping, given that UPS, USPS, Fedex and everybody involved in the transportation business is making sure they're wasting the least amount of gas.