Because they're uncomfortable and tiny. I can't do groceries in them, if we want to bring my son anywhere we need to take a different car, they don't work well for long road trips, speed bumps (heck any bumps) in the road are a huge pain in the butt, when the top is down I'm stuck pulling painful knots out of my hair for a week, and if I sit with my legs to the left how I'm comfortable, the console digs in to my legs.

I know some people like them, which is fine. Sharky loves his miata so I'm happy he has it and I'm happy it makes him happy. It just isn't the type of car for me.