In the way that Swagger / OpenAPI is for API endpoints, but most of the "skills" you need for your agents are not based on API endpoints
Why not just extend the OpenAPI specification to skills? Instead of recreating something that's essentially communicating the same information?
T minus a couple years before someone declares that down-mapping skills into a known verb enumeration promotes better skill organization...
Because approximately none of what exists in the existing OpenAPI specification is relevant to the task, and nothing needed for the tasks is relevant to the current OpenAPI use case, so trying to jam one use case into a tool designed for the other would be pure nonsense.
It’s like needing to drive nails and asking why grab a hammer when you already have a screwdriver.