Modern knitters are often a bit shocked to hear about sock seams that run under the heel (and even, under the entire foot, as in this example from the American Swedish Institute.) It's from the 1920s or the 1930s.
It's hard to see in this photo, but I swear the seam is there. It runs all of the way from the top of the cuff, down around the heel and under the foot to the toe.
I think people did have tougher feet back then. Shoe style and fit expectations can change how a sock really "needs" to fit and feel, too. But, people also had different expectations of their clothes. Now, comfort is the most important element of most of our clothing. Then, practicality, cost, durability, and style were all more important, usually, than flat-out comfort.
Socks with seams down the back and sole are easy to make on a regular knitting machine (someone, please correct me if I'm wrong). That made them inexpensive and widely available. But, it also explains why hand-knit socks were such a focus of knitting for war efforts, even during WWII. Most hand-made socks wear better, generally, and provide better padding in heavy boots than most machine-made socks, especially if you are comparing a sock with seams to a sock without seams.
I grew up wearing machine-knit socks with seams across the top of the toe. It never bothered me - until I tried my first pair of hand-knit socks. After that, there was no going back!