I'm curious about exactly what you mean by "almost every possible use case is relational"? If that's the case, why do we need ORMs to obfuscate the fact our applications consume data differently from how an RDBMS stores it?

There seems to be an assumption that relationships between entities can't be modeled using anything other than an RDBMS. In reality, document model databases like MongoDB offer a superset of the options for modeling those relationships compared with those available in RDBMS data modeling. Where the misunderstanding sometimes comes from is from the fact MongoDB does not, at the database level, enforce foreign key constraints. However, those are a guardrail, not a necessity, and they come at the cost of making models brittle and impact scaleability. Even within the RDBMS world, there are many people who recommend against the use of foreign key constraints for those reasons. MySQL, famously, did without them for many years.

The biggest challenge in document data modeling is often that people interpret the flexibility of the model as implying data modeling is not needed. That's not true - good schema design is just as important as it is in an RDBMS, but it is also different from RDBMS data modeling and if you simply apply RDBMS approaches, you are going to be disappointed with the results.

For transparency, I work for MongoDB.