Probably because most produce was grown locally, not shipped across the country so readily. And if it WERE shipped that far, it was usually so expensive, most families didn't have it regularly.
Even as recently as 25 years ago, most places didn't have produce from all over the world, like regular supermarkets have now. I remember going to a produce place in NJ, where you could get almost anything you wanted, any time of the year, but you paid DEARLY for fresh strawberries and tomatoes in the dead of winter, so it wasn't something most families ate, on a regular basis.
Excellent point, thank you!