What Is The Issue?
This is because The Media Plan objective and the ad type you are looking to create do not correspond. Only ad formats comptabile with your Media Plan objective will be available to you.
What Causes The Issue?
Per Facebook's technical specifications, each campaign objective has a specific list of ad types that can be used. If the ad type that you wish to use isn't available in the Bulk Creator, it means that it cannot be used with the objective you selected at the campaign level.
Due to Facebook restrictions and for technical reasons, you can’t change the objective of your Media Plan once it has been created, so you will need to create a new Media Plan with a different objective that corresponds to the ad format you are looking to create.
How To Fix The Issue
Here’s a grid showing all Media Plan objectives along with the types of ads you can create using them: