You can run fibre between all the exchanges (FtN - Fibre to...

You can run fibre between all the exchanges (FtN - Fibre to Node), that gives a backbone, but has the problem that you only have fibre between exchanges - not down every street.

If you are going to go to the trouble of laying fibre down every street in every metro or semi metro area it would be much easier to run the loop to each house as you go (since you have work crews on the street anyway). It also means the old copper gear can be removed from the exchange entirely, which will remove a lot of maintenance headaches.

The bigger problem is international capacity. If we have a large number of high speed connections, the bottleneck becomes our international links.