They both have replication, which allows them to be multi-node.
But yes. Postgres remains an amazing choice, especially with modern hardware, until you also have the money available to tackle said write throughput issue.
Or a central bank switch may only have 4 major banks.
Or a system like UPI may have 85% of transactions flowing through 2 hubs. Say 50% through PhonePe. And say 35% through Google Pay.