This is surveyor bias as well..That's a stupid conclusion by the surveyors. If 10% don't tip, then 90% are tipping.
If i get 15 fares a shift... i can't have more than 2 giving me food in a shift. Usually i get offers for free food within minutes of paying for food...Millennial tipping is 10% or lower. It's much easier to get them to buy me food than a $2 tip.