Monarch's EDI routes are and always have been for tour operators like TUI and Thomas Cook. I think its highly unlikely Monarch Schedule will be coming to EDI anytime soon, so the decision on MON being at EDI is down to putting in a good price when the tour ops are looking to get an airline for the route.
Jet2 on the otherhand are operating EDI in there own right and see potential in operating flights from the airport.