The model may still become a bottleneck if objects are tightly coupled and you can't scale out the model in a horizontal way. The low level nature and conceptua

The model may still become a bottleneck if objects are tightly coupled and you can't scale out the model in a horizontal way. The low level nature and conceptual simplicity of the relational model allows database vendors to pull some pretty amazing tricks with scalability and clustering. People aren't building big database centric applications because they don't know any better (so I would hope). It all depends on the context. It shouldn't be the default because it can be inflexible.