The client in LPP-38075 has requested that we look into the possibility of scoping a workflow by individual page and not just by site level portlets. They present a page-scoped message boards portlet as a possible example of what this may apply to.
PTR-1818 has related discussion to this topic. I've set the component to Pages due to the following comment from the Workflow team, but please feel free to adjust this value:
This question comes from the customer's requested use case specifically: Should the user be able to define a specific workflow for a specific page, not just for a specific site?
In this case, you should create a feature request for site pages team, in order to use the workflow per page.