I think the placement of the number on the front is leftover from recording mechanisms.

You may remember (or maybe you don’t) that cards were embossed to enable carbon copy replicas, the method of generating receipts. Following that, the magnetic strip was added to allow an additional recording method. Similarly, the chip introduction has replaced the magnetic strip. With the strip and the chip, having the name and number on the front isn’t necessary any longer.

I suspect the threat of loss from shoulder-surfed cards is much lower than digital fraud, and this isn’t considered significant enough to make a difference.