So because it's a task so physically demanding that you are incapable of doing it, that makes it less tip-worthy? That makes zero sense.

He also stated that their policy is to deliver curbside or to a driveway, so the additional labor is definitely not expected or already paid for with whatever delivery charge the customer paid for under those terms.

I'd assume that a big part of why it's less common to receive tips for this type of delivery is that tipping for food delivery has been normalized. A lot of people don't get lumber delivered on a regular basis and probably don't even think about tipping, don't know how lumber delivery personnel are compensated, and don't have any established etiquette for it.

The whole guessing game with tipping is really dumb.