Fifteen years ago when I finished my basement I put two top coats without primer on new drywall. It looks great today. A nice finish without any problems with the paper a joints.
Fifteen years ago you were painting with much different paint..
Many solvents have been removed from today's low VOC paints, the result has been paints that are much less forgiving of surface conditions, for example drywall dust is more likely to cause blistering and peeling of the paint film and the paint may not be absorbed into super sanded mudd joints.
As professionals we have all seen changes in the way paint reacts to different surface conditions, and mostly the changes have been negative.