Painting contractors and related painters get a great discount from SherWill, BenMoore, PPG, etc paint stores and then mark up the paint so they can make a nice margin on the paint- that's why most if not all of the painters in the above jobs recommend SW, BM, and PPG paints- it's a beneficial relationship.
Behr paints (HD) and Valspar paints (Lowe's) don't offer that same business relationship to painters- hence their dislike of it. But they're great paints.
Objective, scientific testing of paints for durability, fading, chalking, peeling, etc., show very good performance from Behr paints.