When you add a workflow you have to add its schedule to share the results in collection menber's. A workflow can be in several collections and therefore different users can schedule it. (why not) This results in multiple schedules for the same workflow. There is no reason why a workflow cannot have multiple schedules.(mandatory in some cases)
Automatically adding schedules to the collection would allow users to see that there is already a schedule on the workflows in question and not to recreate one!
it should also be possible to create a schedule from the collection.