> I can't tell if they're operating on some kind of deep insight that is way above my experience and I just don't understand it

This is answered at the very top of the link on the post you replied to. In no unclear language, no less. Direct link here: https://github.com/prisma/prisma/discussions/19748#discussio...

> I want to elaborate a bit on the tradeoffs of this decision. The reason Prisma uses this strategy is because in a lot of real-world applications with large datasets, DB-level JOINs can become quite expensive...

> The total cost of executing a complex join is often higher than executing multiple simpler queries. This is why the Prisma query engine currently defaults to multiple simple queries in order to optimise overall throughput of the system.

> But Prisma is designed towards generalized best practices, and in the "real world" with huge tables and hundreds of fields, single queries are not the best approach...

> All that being said, there are of course scenarios where JOINs are a lot more performance than sending individual queries. We know this and that's why we are currently working on enabling JOINs in Prisma Client queries as well You can follow the development on the roadmap.

Though this isn't a complete answer still. Part of it is that Prisma was, at its start, a GraphQL-centric ORM. This comes with its own performance pitfalls, and decomposing joins into separate subqueries with aggregation helped avoid them.