There are a few reasons Page Wrappers may not populate as a choice as expected:
  1. The Page Wrapper was created but not published.
  2. The security category may be set to something that is not compatible.
  3. Page Wrapper is cached.
If you have confirmed it is published and not a security category issue try logging out and logging back in.  Once you log back in the Page Wrapper should be listed as an available choice.