I think the confirmation bias plays to a point. I remember getting a metallic baby-puke lime green KIA Soul as a rental car a few years ago, and oddly enough actually enjoyed driving it. After turning it in a week later, I noticed that for about the next 3 months, I saw the "same" car at least 3 or 4 times a week
somewhere in town.
I had a similar feeling as a teenager with my attention shifting to wanting certain cars (Camaros, Mustangs, Dusters, Challengers, Satellites, etc.), that all I could see for weeks were those cars driving around... taunting me, it seemed.
My focus had definitely shifted each time, because I noticed less of the others when I was Jonesin' for a specific model.
Years ago, after I got my '71 I noticed 5 other '71-'73s in-town, and heard about 3 or 4 more potential projects hiding in back yards... and even 2 more at my favorite salvage yard in the 'reserve' lot. Whenever a new one crops up, I usually tend to notice it very shortly afterward.
So yeah, I believe the 'confirmation bias' definitely plays a role, but those cars also have to be "out there" to be seen, after all.
'69-'70s are more revered, and therefore I believe are less likely to be regularly driven, as Mike says. But even so, I tend to see more '68-and-older Shelbys and Mustangs alike at local car shows, than '69-'70s... and I personally know 2 people with '70 Mach 1s, a '70 restomod (Boss 347), and at least 1 legit Boss 302. The one guy I knew with a '69 moved to San Antonio.
Currently, I'm aware of 6 '71-'73s in-town - 2 in the salvage yard, 1 for sale project coupe, Auron1973mach1's car, 1 owned by a driver at Steak Express (saw it running and talked with the guy), and mine - with mine definitely being the only in any kind of 'restored' shape (currently). (the blue '73 coupe and '71 M-code pewter and black Mach 1 I showed pictures of awhile back were both sold and left town years ago)