The common here is the set of customers willing to sign up for a subscription nobody owns these people. Staring another service (adding another cow) is a gain for the service owner, but the set of people willing to pay for subscriptions goes down.
If your favorite show goes from service A to service B, you might switch, you might maintain both subscriptions, or you might decide neither is individually worth it, and either stop watching or start pirating.
Even if service A does not lose shows, its no longer getting shows at the same rate, so the quality of that service goes down, with nothing of similar quality to replace it. So again some customers will stop paying and the commons shrinks.
So, I'm considering this, but I really don't see it.
Yes, there's a shared, limited, resource pool. But that's true of any constrained economic resource.
The element of privatised gain / socialised loss is what's missing. Any given entrant has an all-or-nothing proposition. But gains precisely match others losses, assuming a fixed pie.
The marginal/average cost dynamic is a red herring here, so far as ToTC goes.
The privatised gain is that a content producer who was previously licensing their content to a streaming service, and starts their own streaming service, makes more money streaming than by licensing.
The socialised loss is that fragmentation of distribution makes people less likely to pay for any service. By trying to take a bigger slice of the pie, they make the pie smaller.
If your favorite show goes from service A to service B, you might switch, you might maintain both subscriptions, or you might decide neither is individually worth it, and either stop watching or start pirating.
Even if service A does not lose shows, its no longer getting shows at the same rate, so the quality of that service goes down, with nothing of similar quality to replace it. So again some customers will stop paying and the commons shrinks.