"Retarget skeleton on existing Anim Assets" menu option doesn't show consistently.

When I right mouse button click on an Animation Sequence in the Content Browser. Duplicate Anim Assets and Retarget always shows up under:

Retarget Anim Assets > Duplicate Anim Assets and Retarget

While Retarget skeleton on existing Anim Assets does not under:

 Retarget Anim Assets > Retarget skeleton on existing Anim Assets

Does anyone know why this is the case?