I think like some others have said this isn't to try and scare people off but to prevent congestion at the Airport and a quick call to ascertain that all is good would be fine so very unlikely they'd knock you back. Unfortunately, they can't put in "Please give us a ring before you come on in" and have to keep to more "official language" like this that sounds unfriendly.
I remember many moons ago heading into Uluru as we couldn't make Alice Springs due last light, ERSA entry had me all kinds of scared with all the requirements for prior notice etc.., security rolled out as we were pulling into a parking spot and waved us to a different spot so I was getting a bit worried at this point we'd get a yelling at, fined or what have you. Turns out it wasn't marked but was a preferred spot for RFDS and the security was the nicest bloke I've met at an Airport, could not have been more helpful and accommodating!