Why doesn't BGP...

My cruise control works quite well. So could routers.

IGRP/EIGRP has a knob that you can turn on to have it take congestion
into account when making routing decisions. Its off by default.

You know why its off? Things get really unstable otherwise.

But if someone really really wants to play with this sort of thing,
go ahead & turn it on - on your *own* network. Make it work there
first - a couple of Phd dissertations later & folks may be interested
in turning it on in their own networks & maybe in the Internet at
  --asp@partan.com (Andrew Partan)