And for good reason. If people already call command completion bloat, imagine the uproar if they found out that bash or zsh is built in and the default shell.
FreeBSD is often used as the base for appliances, so some downstream users it may indeed be unnecessary code to maintain. (You perhaps get 'extra' CVEs against your product that may increase maintenance.)
For those with CLI access, adding a more full-featured shell is fairly easy with pkg.