The tragedy of the commons is not just any nonrational behaviour. It's a specific case where there is some property or resource
held in common, and actors or agents can act to
privatise gains whilst
collectivising costs.
The classic case illustrated in Garret Hardin's 1968 essay is a common field, with a fixed carrying capacity, at that carrying capacity, in which one herdsman chooses to run yet more cattle. The total yield goes down, but the defector's yield increases. Since the gain is private and the loss is shared, the net incentive is to overgraze.
Calling the subscription spending market a commons seems a stretch. That's never a shared resource, it's always one which accrues to specific provider(s). Though the tendency is for it to accrue to a winner-takes-all provider.
And more crucially, there's no socialised loss here that I can see. There is a race-to-the-bottom dynamic possible with excessive competition, so long as offerings of one providers catalogue cannot be shared with others.
The problem instead seems to be simply one of falling marginal costs, such that the largest provider has the greatest efficiencies, and that with a sufficiently subdivided market (multiple subscription services), no one provider has a sufficient catalogue to sufficiently interest any one viewer, but the monetary and other costs (choice, selection, management) of multiple services is too high for any one subscriber to choose more than a small subset of services.
That's not a tragedy of the commons, it's a natural (network effects) monopoly situation.
(I'm aware you're not the original poster. I'd hoped they might respond.)