Licensing is the direct cause, but greed is the reason there were exclusivity agreements to begin with.
I disagree. Networks seek exclusivity agreements to reduce risk, it's standard business practice for large companies. Without there's a chance their investment will be suddenly worthless as another network shows the same content, so they pay a premium for certainty.
Of course everything in capitalism is greed in some sense, even the salary you as a worker can ask for from your employee. There's a fine line between standard market practices and profiteering.