using letters thins out the possible meaningful namespace, but 32 bits human readable has been a tradition for a long time, macOS has used this format for file type magics forever and i've also used this format in my own binary encodings
totally there would be a way to compress them into a single number meaningfully, probably you could even have them as long as 6 characters and have almost no collisions just by simply summing the ascii code of each letter, and you can compress it further by allowing 3-6 instead of all 6