Programmers were much smaller in numbers, most of them probably enthusiasts, and they pretty much had to understand many more low level details of their machine

Programmers were much smaller in numbers, most of them probably enthusiasts, and they pretty much had to understand many more low level details of their machines to effectively use them. Those machines, like the PET here, were also many orders of magnitude simpler than today's computers. Chances are, someone who actually needed to do "WAIT 6502, x", which is a pretty bespoke statement especially if there is no widely documented device or (interrupt-modified) system variable behind it[1], would be able to figure out the easter egg. And then probably race to publish it in a magazine somehow, so that its existence could be repeated many many times in the press over the decades, which is pretty much what happened. [1] If that were the case then the easter egg couldn't be there almost by definition.