Contribution Pages "Membership" settings not recognizing existing Membership Types

I successfully created and configured three Membership Types in CiviMember.

I created a Contribution Page to use as a member signup form. When I did so, the "Memberships" tab was disabled/grayed-out. When I clicked it, I did NOT see the "Membership Section Enabled" checkbox. Instead, I saw a message stating:

"You need to have at least one Membership Type to enable Member Signup."

That message linked me back to the Membership Types page where I can plainly see my three existing Membership Types. Did I misconfigure my Membership Types in some way so that they are not being recognized by the Contribution Page's Membership Settings config?