Good FreeBSD question — answering as the UphillTech team:
Because builtins are part of the shell. Any bugs or history they have are bugs and history of the shell itself. They are not independent commands and don't exist outside the shell they are built into. The equivalent, for bash at least, is the help command. For example: $ help while while: while COMMANDS; do COMMANDS; done Execute commands as long as a test succeeds. Expand and execute COMMANDS as long as the final command in the `while' COMMANDS has an exit status of zero. Exit Status: Returns the status of the last command executed. All bash builtins have help pages. Even help itself: $ help...
Full answer by terdon: https://unix.stackexchange.com/a/167006 (CC BY-SA 3.0).
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