Ford did that on purpose. Presumably so there would be less wear on the 'reverse' parts in the transmission, from having to shift thru reverse at most startups to get to Drive.
As improvements to the automatic transmissions were developed and beginning in '58 (or maybe '59?) the neutral safety switch was also upgraded to allow starting in Park. .
Borg Warner designs were that way back to 1951 in FoMoCo vehicles. The early 39 hydramatics didn't have a park position. The operator was instructed to put the selector in reverse to lock the driveline. Starting was in neutral. After parking pawl type locks were introduced, the park selection was added. Many still started in neutral or were started that way out of habit. This changed quickly after transmissions were allowed to start in park. Folks don't even think about starting them in neutral anymore.