I'm not sure that's the whole story. A critical point is that this is a B2B site. The people shopping here would tend to have a need in mind that can be solved by finding the exact right part that meets their specifications.
By comparison, the typical consumer shopping experience is much more one of discovery, not need-solution mnatching. Keep in mind the average HN user is not the typical shopper. You and I might like to "get in and get out" but so many consumer shoppers LOVE to go to a place like Target or HomeGoods and browse around aimlessly, window shop, discover, explore - and that indicates a far different type of UX than what B2B would look like. These shoppers value stimulus, sparks of ideas, reviews and testimonials, and all the other "cruft" that was removed from McMaster.com