Hi Michelle,
It boils down to the Program enrolment plugin - YOURTOTARA/admin/settings.php?section=enrolsettingstotara_program
"The Program enrolment plugin is used to provide access to courses that form part of a program".
So if the trainer isnt assigned to the Program, the plugin isnt used with the result that the courses are "unavailable".
The changes necessary to make your idea work are not simple or trivial and would need to be carefully thought through as it could completely break all sorts of enrolment/completion/reporting existing functionality.
If you would like me to file an enhancement request let me know.
cheers,
George.