The problem ranges from range to speed to purpose. The cn-235 was designed primarily as a military cargo transport with the ability to transport troops. A search of it's history will reveal it is great in this role. If you look at the rear of the aircraft you can see the tell tale signs of this. All the tail feathers are raised to allow a rear cargo door as needed. Because of it's original intention as a military transport certain aspects of performance were considered sacrificeable. Speed was the big hit. It's slow compared to most of the other aircraft in the 40-50 seat range. Looking at Jane's books you loose about 30-40 knots in cruise. Range also seems to be a problem. The more you load it up with weight the shorter it's range. It's because the wing is designed to get good loads out of unprepared (rough)fields for a prescribed distance which was predetermined by a military board. This is somewhat opposite of what airlines seek in a commuter(regional)aircraft. The only exception seems to be the early Dash 8's. Even De havilland had to fail with the Dhc -4 Carribou and, Dhc- 5 Buffalo. Both were good military fourty seaters but fell short on efficiency for paying passenger purposes. In the end, this plane is a success. It has garnered some market share that's not military. It's well suited to hot, short, rough runways. Otherwise there are better choices in this market. Politics helped to but, that's a whole other story!