I do know where you are coming from - I model the mid '50s and want to have a reasonable amount of normal everyday Fords, Chevies, Plymouths, Mercury, Chrysler and Buicks and the odd Studebaker, Kaiser, Hudson, and Packard about . . .
But, let me argue the other side of the coin a bit. Diecast manufacturers make what will sell: not much market for a Plymouth Savoy or base Chevy coupe, compared to an Eldorado or a '57 Corvette.
More important thought, most of us model what we like. For example, my layout abounds with nice shiny Warbonnet F3s, and has lots of big articulated locos - BigBoys, Challengers, Alleghenies, Yellowstones, Mallets, etc., and big, big Northerns and Blue Comets and such. There weren't that many of those around way back when. There were a lot of tired, old, worn, wheezy junker locos about however, but on my layout? Nary a one.
It's the same with the cars, too. In the two and one half blocks (maybe twelve feet max) of my tiny little downtown Sn Beattdaise mainstreet and the stores and parking lots about them, I have with a fair number of 'normal' cars . . . and only one Cadillac. But I have two Truimph TR3s, two Austin Healey 100s, an XK120 and a Jag sedan and a C-type too, an Aston Martin, a Cunningham, an Allard and a Morgan 4+, an Fiat 8V, an Alfa Guiletta coupe and five '50s Ferraris (two 212s, two 340s and a 375), two Porsche 356s, two T-birds, and two Corvettes. Strange little town, this one I model . . . Sports cars just about outnumber normal cars - I'm a car guy and I like sports cars, so . . .
Photo of part of my mainstreet from last year shows unrealistic "demographics" of cars on its downtown street. Probably the most unrepresentative thing here is not that you see a Jag XK-120 parked across the street from a Ferrari convertible (red on the extreme left), but that you see even one Chrysler Airflow (the gray sedan in the middle foreground). There is the '54 Caddy on the right . . . and two harleys and a Vespa for good measure!