Why doesn't BGP...

Seriously, the load-sensitive traffic management _can_ be done,

Can't be done with ciscos, or any existing routers...

Just the other day an engineer was telling me that he was adjusting
metrics to better balance load and account for congestion. I was
doing the same last week. As always, it seemed to work quite well.
So it can and is being done. It wasn't enough of a mental effort that
I believe that computers couldn't do it better.

I agree that "make small changes slowly" is good advice.