I'd guess that the primary difference is in the attribute space and specificity. Home Depot products are specific in odd ways. E.g. an 8' PVC pipe can be short

I'd guess that the primary difference is in the attribute space and specificity. Home Depot products are specific in odd ways. E.g. an 8' PVC pipe can be shortened on-site, a 3' downrod for a ceiling fan might not be able to. So substitutability is hard.