Insurance and Pilot Capabilities
I suspect one of the reasons you don't see "fast" pistons is the cost of certification and insurance.
As mention above, Jets are easier to fly, and Twin Turboprops give a higher margin single engine, but piston twin proficiency requires constant practice.
The difference between a Professional (Doctor/Entrepreneur etc) who flies, and an Professional Pilot is huge, the investment in time and money to achieve the same level of proficiency is more than most "busy" people are willing to spend.
So there's no demand, and the price of each item goes up to the point that it's cheaper to buy a used TBM than a new piston-powered 350HP rocket ship.
Been there, done that.