I can't figure why shops don't provide it. A friend of mine has done entire exhaust systems with the cut and weld method. The system looked good.

 

I really don't know why either, but I have a few possible reasons, one of which I know to be a fact since I had asked the local Exhaust Works owner about it when I had them install the TTI exhaust on my Roadrunner. He absolutely loved the TTI exhaust by the way, he mentioned how he gets lots of cars in and the owner supplies a Flowmaster, Dynomax, etc. exhaust system that is supose to be a direct bolt-on and it didn't fit quite right. He liked it so much that he made sure to get the name, address and phone number of TTI before I left. One of the biggest reasons was the cost of a mandrel bender and the low demand for it. Most people just go in for a straight up replacement exhaust or repair and would never even notice the power difference between their factory mandrel bent and the replacement compression bent. The gains will only be noticed on a dyno and at the track, the difference usually isn't big enough to be noticed by the seat of your pants/butt dyno.