The reason is the aftermarket knew it's more money to them to use the 9 inch ford. That's why they make all the **** for them.
They aren't lighter, they take more HP to drive and they cost more money to get equal strength. It's all about the money.
And the BIG lie, which is...if I use a 9 inch (same for an 8.75) I can set up a second (or third) third member and change them out. I can have a highway gear, a city gear and a drag gear. I've been doing this fpsince 1980 and I've never, NOT ONCE seen anyone that runs below Comp Eliminator ever change a gear set at the track. I'm sure it happens, but it ain't a regular deal.
And street car guys damn sure ain't doing it. It's a royal PITA, and it isn't fun to do.
