"Object-relational mapper" is a misnomer, they should be called network data model to SQL mappers. They're not primarily for mapping between different arrangements of the same data, but about recreating a network data model perspective. How many ORMs support composite primary keys and non-binary relationships?
As you said, the challenge of understanding math is why the relational vision failed, but also why the industry keeps reviving the network data model.
As you said, the challenge of understanding math is why the relational vision failed, but also why the industry keeps reviving the network data model.