Why are original chinstraps so rarely encountered?

Certainly time has a lot to do with this but I think it is mostly because the M91 chinstrap connection post system was a crappy one. The fittings had an in-exact fit and the chinstrap was prone to coming loose on either connection end. When the M16 helmet was being designed, the chinstrap connection/style was almost an after-thought.

It was patterned after the chinstrap mounts found on the M1891 enlisted spike helmet. Those chinstrap posts served well with the spike helmets as 99% of the time, the chinstrap was held taught around the front of the spike helmet visor, rather than actually used as a strap beneath the wearers chin. In the case of the steel helmet, the chinstrap needed to be functional in that capacity but the M91 connection post fell short in its ability to do so.

By 1918, the Germans designed the much better suited M18 chinstrap which was permanently mounted to the liner band. The M18 helmet is far more rare than the M16 but when examples are found, there is a higher ... more.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.