The moat
Residual brand and a large user base, especially internationally. Network effects have inverted in the US checkout. Venmo is a consumer network without a full business model.
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.