I expect when the hex format was designed ( 1973 ? ) most systems tended to only really use upper case. I can remember that the fast chain printers at work only did uppercase characters, having lower case on the chain would have really slowed the printers down. Mind you I did not want to be near them when they were printing due to the noise.
The file I came across was from doug rice and was generated from the rcasm assembler. I was looking at various cross assemblers - his pages are a mine of information.
Hope you have a happy Christmas and new year
David