[Steve Chryssos]

I have a 68, so maybe I can be objective:
-They are the last of the 1st gens as well as a one-year-only body style.
-The squared off wheel arches make it easy for them to look lowered without as much work.
-The headlights are pulled in towards the center of the vehicle, so they look inherently wide.
-They are in fact wider than the 67/68's
-Legendary 69 DZ302's had all the right goodies--considered by most to be the high water mark for Camaros.
-In 69, the Camaro was still a relatively new platform. But it was just coming into its stride. So most enthusiasts connect with that year.

I'm sure there is a long list of reasons including numerous high visibilty 69 Camaro hot rods and one legendary race car: Mark Donahue's dominant Penske Racing 69 Camaro.