Mallabe intentionally restricts image manipulation to one image at a time to avoid the complexities and challenges associated with bulk operations - these include error handling and variable timeouts that can occur depending on the user input.
The execution of bulk operations depends on the platform you are using (e.g., Zapier & Make).
Utilize Iterators: Make Iterator Module
You can the video below to understand how to use it.
https://www.youtube.com/watch?v=L31sGpGLLcE
Utilize Looping: Zapier Loop Action
You can the video below to understand how to use it.