The moat
Brand, scale in content amortization, and data for personalization. Switching costs are low (easy to churn) which is why this is not a fortress. Habit and catalog depth substitute.
Pain, risk, or retraining required to leave.
The product gets better as more people use it.
Patents, data, licenses, process knowledge, regulation.
Fixed costs spread over a volume rivals cannot match.
Structural ability to be the low-cost producer.
Pricing power from trust, habit, or identity.