If turboprop engines are more efficient than turbofan/jet engines at lower speeds, and have a lower specific fuel consumption, why are there no large passenger airliners that utilize the turboprop engine?
I expect this would increase flight times, but say for example an airline was to only operate short-medium haul flights within Europe, wouldn't it be in the interest of minimum fuel burn to use the more efficient engine, the turboprop?
Most modern airliners seem to use two turbofan engines. I am curious as to why the largest turboprop aircraft have a passenger capacity of below 100 (ATR 72 and DHC Dash 8) and why there are no 150+ pax turboprop airliners.
With minimum fuel burn as the priority, ignoring costs and flight times, would this be a desirable and achievable design option?