I realize this is a rhetorical question likely intended to be a joke, but the answer as with most historical things you can find on HN was technical trade-offs that made sense for the time: for a file system intended primarily for floppy disks (where the total available space was likely reported in KiBs at most), it made sense for the file system to be as space efficient as possible. Directory entries were allowed (exactly) 32 bytes only, and after necessary metadata (last modified date, status flags, where the contents are on disk [clusters], etc), 8+3 (11) bytes (~34% of the 32 bytes) was what was left for the name.

https://en.wikipedia.org/wiki/8.3_filename