@icarushector
It's been popular a lot longer than just the 30's. For a few examples
President Richard "dick" (called Tricky Dick on Monday night football) Nixon
Vice president Richard Bruce "dick" Cheney
Richard "Dick" Grayson (original Robin from Batman)
It's just a weird thing like Margret turning into Peggy, William turning into Bill(Bill Clinton is a good example of this), or Robert turning into Bobby. It's not really as uncommon as people might think.