In the commercial world, and upper-end business aircraft, VERY HIGH reliability and ever-improved fuel burn are paramount, because of their effect on operating costs. Airlines effectively underwrite the engineering and certification costs of manufacturers to achieve these ends.
In the private/training aircraft market, the cost pressures of the airline market just don't exist; ergo no such underwriting of the manufacturer's costs.
(Just send me a freshly overhauled R-985, an 85+ year old design, and I'm happy!)