The main reason is becaus the sprial hook puts *much* more stress on the bearings in the head of the mixer, when you
see the KA in action with the sprial hook, you can see how much more intense the mixing is, vs the "C" dough hook that
in my mind, should never have been even put on the market.
That being said, - I do believe that if you don't stress the mixer, you could prob get away with using the sprial hook.
Me ? - I may take the plunge and buy the spiral hook, but would limit my dough mixing to enough dough for 1 medium pizza.
I've had my KA mixer now for, hmm, maybe 12 or 13 years, and it is still in mint condition. I wouldn't want to ruin it in a few months
by stressing it. ( I also have the DLX mixer however, and use that now for all pizza doughs ) ( but being a gadget guy, I do like that sprial hook )
That sprial hook is a thing of beauty isn't it !
It's funny, I was just thinking about this just yesterday. I've been considering doing the exact same thing you did and was going to start researching this morning.
I have the KSM150. My dough batches are generally in the 500-900g range. I can't see why I would have a problem using a spiral hook with my machine. I wonder why KA doesn't recommend this.