It might come down to appearance too. The Camaro just has that look and stance. Not that a Z06 doesn't look cool and mean...but to me Corvettes are styled more for business (Aerodynamics, etc...) and less for menacing looks. When you put the two cars next to each other and judge them on looks alone and don't consider any weight or performance aspects, I think a lot of people would choose the camaro's styling over a Vette.
But I have contemplated the same question in my head. I've done some searching for used ZO6's and have found a few nice ones for around 45K. Pretty hard to not see the ZO6 as a better buy for performance at that price when it's much lighter and has the LS7.