because ds-3's to naps are finite resources and cost money.
why would you assume that any provider wants to burn his ds-3
by taking traffic at a nap when he has better connectivity
to your transit provider? in fact, he may not even peer with
your transit provider at the nap.
why am i not free to arrange traffic flows between my backbone
and others as i see fit? mci and sprint have arranged six ds-3's
between their respective backbones. if your transit provider is
sprint, i don't want your traffic to me by way of a nap. if you
give it to me at a nap, you deserve what you get.
one would think, in my case, that a ds-3 to a nap would cost
me more than a direct ds-3 connection to the XXX backbone.
(assuming that XXX is the transit provider).