If nothing else, it is patently wasteful and, as a user, you don't really see CI billed in terms of network bandwidth. Just indirectly through the equivalent of mainframe minutes. And even then, that's not enough to discourage anyone from building a suboptimal pipeline.

It used to be possible to have a squid or even a backwards varnish cache handle lots of this but https everything has made that much harder to do. Still possible, however.