Leaf-and-Spine Fabrics beyond Data Center Networks

Why don’t we use Spine Leaf design for service provider transport networks? Is Clos design only for DC why can’t we use outside DC?

It would be interesting to hear about leaf and spine architectures in an enterprise/campus network. I assume that the service provider case is very similar, but a large enterprise or campus has different operational and security models. Possibly a place to discuss how Charles Clos has taken over the networking world now that switches are non-blocking. Bell Labs and the carriers strike back! :-)

It would be interesting to go over adapting leaf and spine for ISPs or probably IXPs. Most of the materials that are currently available are focused on the datacenters with more of compute and storage nodes not ISPs and service based fabric. What do you think?