The small GA aircraft turbine engine market is a tough business. It's expensive to develop, certify and tool up for a new engine design. The small turboshaft segment (ie. the RR250) is very few numbers and relatively low price, so it is difficult for an engine OEM to recover their non-recurring costs. That's why you see little significant (non-military) development occurring with these engines.
Even in the large commercial turbofan engine market, the OEM's don't make much profit on the sale of new engines. Most of their profits come from
sales of spare/replacement parts.