There are three main issues with two potential organizations "not cooperating".
1 - Getting slots at the canal bridge and cooperation from the Army Corp
2 - Interfacing with existing MBTA service to run what is essentially an extra service. MBTA is in the middle of some changes to how they schedule trains, and their regular service is going to take priority over what the CCRTA wants to do.
3 - Reality of cost for added service and availability of resources to run that service from the MBTA. Again, their focus is their regular service.
I guess Mass Coastal could be an outlier as an issue, but I sincerely doubt it.
EDIT: Based on the Facebook comments it looks like #1 is the issue. They were looking to move to 2 round-trips on the weekend instead of a down morning/back evening. Would allow a day trip from the Cape to Boston.