My earliest background as a shell user was as as system administrator (back in "the day", let's say), and forks are always potentially expensive, and often the reason you're opening a shell session in the first place (to diagnose resource contention or exhaustion, for example). There have been lots of times when one more fork is too much to take. (Which also, yes, makes it "interesting" to figure out what you can run in your shell session, too).