They burn more fuel, cost a considerable amount more to acquire. IDK what your definition of good is but our company just bought a quality one a couple months ago. It has nothing to do with the metro being "my love child" it literally makes zero sense to operate. If a metro is blowing out on a route, so will a 1900.
They bought one. Try procuring enough to make a fleet of airplanes. There just aren't that many out there.
It obviously makes >0 sense because several freight companies operate them and they fit a mission that UPS/FEDEX/DHL wants.
Maybe from a MX prospective PT-6s are easier to maintain then the garrets. I'm not sure on that though so I won't comment.