I would guess that providing potential building blocks might reduce the overall complexity of the search space and could thus yield results in a reasonable time frame.
It would be also be a bit similar to “manually” manipulating a model a la: “what if I put the batchnorm layer before the ReLU?”
That being said, I’m not deeply familiar with the latest research in this direction, but a complete generation of a model “from scratch” would be fascinating to see.