Because its about 3 times the price for a straight bit of metal pipe.
The issue with Power Flow Ian is they aren't true custom. What I found out is, they basically stock loads of different angled pipes etc and connect them together, it's like lego.
I think there is someone in brighton but can't remember the company name which will make you up a pipe on the spot.
Failing that, go to Birmingham and go to MIJ Performance
If you're thinking of heading over to birmingham look up RJ Performance for custom exhausts, Jay who owns the place has fabricated many exhaust systems for me and I can recommend him very highly