Why the "--export-secret-key" switch is not listed in help screen?

[Moses]

Hi,

I've notice the switch "--export-secret-key" is not listed in the help
screen (i.e. gpg --help) and I spend a lot of time to find it. It
seems to be one of the most used switch for backup private keys and
sync keys between machines. Could the developer add this switch to the
help screen? It would save users a lot of time.

Thanks.