I think it is a chicken and egg thing. I too looove wherigos, so to encourage development (or at least to discourage grandfathering, which I suspect is more likely), I am trying to put out more wherigo caches. I have released one, and am about to work on another (rather large) one, and have ideas for a third.
If we get more wherigos put out there, and get more people finding them, Groundspeak will see that it is worth investing time in them.