CBS is not in the network business. This is not their network to distribute or sell.
Every article I have read, with direct quotes from top CBS and Cumulus executives, has them all referring to this as a CBS Network with Cumulus handling distribution and spot sales, as well as carrying the programming on 67 of its stations. I have worked at national networks where major rep firms handled a lot of the spot sales, but that didn't mean the rep firms owned the networks, they just collected a commission on whatever spots they sold.
I don't know of any network that requires spots to run adjacent to programming. Even spots in CBS TOH newscasts can run out of show.
I haven't heard the new network yet, but it does promote the fact that it is offering several short feature programs by known sports commentators.
Those are the kinds of network offerings that often have specific sponsors attached to them. Well known non sports network examples of those kinds of specifically sponsored shows include Charles Osgood on CBS radio, and, formerly, Paul Harvey on ABC.
CBS gets paid regardless. Does CBS want to corrupt one of it's highest billers to help Cumulus do it's job? How does that help Moonves? They get 100% of the money if they run local programming. If they run the network, they share the money with a competitor. How does that help Moonves?
If Moonves has two radio stations both blanketing the top market and carrying exactly the same programming he is losing one potential revenue stream. Even if, he has to share some of the revenue on a second stream with a "partner" there will be more money in his corporate pot at the end of the quarter.
CBS has already made that kind of move in other major markets like Philly with WIP. It has already established a pattern. Don't forget, CBS only has to clear X-amount of network spots an hour that will be sold by Cumulus, and then it can sell more local spots on the AMs itself. That certainly increases overall corporate revenue and is more money in the pot for Moonves.
It also appears that the original deal between CBS and Cumulus put certain major market CBS AM stations in as network affiliates, and it is hard to imagine that either CBS or Cumulus wouldn't have made plans for full clearance in the top market. The network needs that for national sales. They both have known what those long-term plans are since last summer, and the FM stations they each have bought since, and the programming choices they each have selected for their new stations, offer pretty good hints of what their longer-term plans in the top market are.