Aluminum exhaust tubes, why not?

[2percenter]

Not meaning to shoehorn into this class again, I was confused as to what this tech forum was specific too, so forgive the rant.
I'll interject with one small note, thin gauge Aluminum tubing is readily available from any good stocked speed shop in many sizes ranging from 2" all the way up to 5" along with many sections which are already mandrel bent. Straight sections are also available of course.
I was just wondering because so many people have to run exhaust systems in other classes and with so many noise restrictions nowadays, Aluminum for the system along with the Mufflers may be attractive to some. The Turbo guys use them for many applications on their hair dryer combos. What puzzled me was; is there an exhaust flow hampering with its heat being evaporated before it reaches the end of the system?
Maybe it's a cost issue.