Just help me understand why this is good practice?
Certainly your example isn't good practice, and from a commercial point of view, discouraging customers isn't a very good idea.
I've some sympathy for airfields trying to persuade visitors to phone for a briefing. Most small airfields have noise-sensitive areas and many have non-standard circuits or joining arrangements; ignoring those can be dangerous. Briefing can sometimes be done over the air, but during busy times (e.g. fly-ins), which are the most critical times, life histories over the air are not on; there isn't always time for an over-the-air breifing.
My point, though, was that airfields can set whatever PPR conditions they choose, and we, as visiting pilots don't have the right to ignore them. I'd regard it as bordering on poor airmanship.