Managed Metadata - can't apply to Site Page

I've created a Term, and added a Managed Metadata column to the Site Pages library of a Team Site but I'm unable to apply any terms to the Page via the Page Details screen.  Looking at the Library Settings, Columns, the column I've created only has 'Wiki Page' in the 'Used In' column; I don't know how to allow it to be used on Site Pages.

I'm trying to create a Managed Metadata column of tags to apply to news articles across all sites in an intranet.