I've given some thought to this, and think people, including myself (in some regards) gravitate toward what is familiar to them. So many more Camaros were sold than first gen birds, although the birds often had more Hp, better track times etc. In their memories they remember their their dads or uncles Camaro. I've heard many younger guys say "I want to get a trans am like smokey and the bandit, they are so fast" when some of the first gens had nearly twice the horsepower. (I will never forgive Burt Reynolds for this!)
I agree with calbird that first gen birds are under appreciated. But this may only be because most people are more familiar with what saturated the market. I like to think I'm more familiar with reality, first gen birds kick but!! I even read somewhere that GM referred to the Camaro as the sister car to the Firebird. Bigger diameter driveshaft, bigger u-joints etc. etc. etc. that's what I'm familiar with!!!!!