BlueWolf: Thanks aa but it was more a question of why not more twins, than of why not more turboprops per se.
I mean I guess it's all been thought through, I would have thought the Russians at least would have experimented with the idea if it was a goer, but it appears not; and I'm curious as to why not.
Perhaps a bit of it is cost and the capability of aircraft of limited utility.
A twin generally costs more than a single. Engines are one of the most expensive pieces of less complicated aircraft. Generally more expensive to design, purchase, fuel, train and maintain than singles.
A capable twin turboprop is going to be larger, more expensive and have more performance, getting you closer to pure jet costs and capabilities, and many air forces seem to be willing to spend a bit more to get pure jet performance/capability. A modern turboprop with good sensors, ejection seats etc. is not going to be cheap.
Capability. A turboprop is going to have some limitations and many air forces would prefer something that can perform both in limited wars and full, near peer or peer level wars. The US and western forces have traditionally been reluctant to invest in limited war capabilities, and have been more focused on near peer adversaries. An aircraft that can not survive and operate on a modern battlefield is of little utility. When these powers find themselves in a limited war, they may find themselves with overly complicated equipment- killing trucks with multi-million dollar jets...we seem to forget this lesson over and over....
Now if we knew we were going to be in a limited war for decades, with a permissive environment (very limited air to air or ground to air threat) a turboprop would make great sense. A modern Bronco would be perfect for many of the conflicts over the past decades. Again we tend to forget this lesson. A twin would offer good performance and reliability.
Finally if you are a believer in the dangers of the military/industrial complex in the US- a simple turboprop does not generate the same level of interest as does a complex order with a multitude of contractors and congressional districts.