Or maybe it's because not all quilters want the same thing. I want a larger throat space but I also want programmable stitches, multiple needle positions, needle up/down, etc, etc.
Juki makes a straight stitch only, high speed machine for a reasonable price. Having a heavy duty machine is not a bad thing when you're doing hours of fairly high speed sewing. I had one and sold it to help pay for the Janome 6600.
Sewing machines are even more of a personal choice than a car. You just have to keep looking until you find the one that suits your needs.