Because sometimes you have multiple, discrete applications which should be isolated, but need high performance (40gbe, optane, huge amount of CPU concurrency, whatever) and don't want to slice up the server for virtualization or run it in the cloud. Or you won't want to manage multiple pgpool/pgbouncer configs. Or you want BGP-based site failover and it's more complex with more clusters, or replicating massive data warehouses/ML data/preprod is substantially faster if it can be a job on the same server instead of replication, or...

I wonder if something like Neon can help here. The pitch is that it refactors the dataplane out so that you can scale individual databases from 0. If it's suitable for scaling multitenant workloads, then it should be sufficient for multiple teams, I assume?

That said, it's a fork of Postgres, and I bet there's plenty of limitations. But I still find it interesting nonetheless.

If we're talking production, it's still trivially easy to have multiple clusters on the same OS without resorting to virtualization or cloud.

As the original post sounded though, it struck me more as a development thing (because why would production allow such access at all?)