It would be good to put a reason for the PPR in the AIP or on the aerodrome website if it applies.
How about
: "Because I say so, and it's my $odding airfield."
Most airfields are private property, and in most parts of the world there is no absolute right to enter private property without permission. In the UK the owner of an airfield has the right to impose PPR as a condition without having to justify it. It's their airfield, and if you don't like it then you don't have to visit.
Yes, it takes a few minutes to phone, and they don't always answer, and I might even change my mind in the air. There can be reasons why I might turn up and call on the radio, even where it says PPR by phone. (And I take the risk that they might turn me away.)
However, I'm genuinely puzzled by the objection on principle raised by some people. I mean: do you expect an unrestricted right of access to any private property? Does being a pilot give you some sort of droit du seigneur over airfields (and the local virgins)?