In the case of one project I've been in, the issue was the ORM creating queries, which Postgres deemed too large to do in-memory, so it fell back to performing them on-disk.

Interestingly it didn't even use JOIN everywhere it could because, according to the documentation, not all databases had the necessary features.

A hard lesson in the caveats of outsourcing work to ORMs.

I've worked both with ORMs and without. As a general rule, if the ORM is telling you there is something wrong with your query / tables it is probably right.

The only time I've seen this is my career was a project that was an absolute pile of waste. The "CTO" was self taught, all the tables were far too wide with a ton of null values. The company did very well financially, but the tech was so damn terrible. It was such a liability.