Most of the important things have been said on the issue. I would also add that it is sort of a scheduling art! It is crucial to have those planes take off sufficiently per day. By flying two frequencies on low pax routes, you get your RI up faster and hence your load factors. But if you are without competition, I do not consider it necessary, also uses slots, you might need elsewhere. In EuroChallenge, which I left today, my airline was based on almost only Saab2000s and I managed to fly down competition on 400pax routes, due to frequency and small a/c. So it is not simply about small pax planes and short routes. The business model simply means that commuter is short-haul. Routes, where people go to work in the morning and come back in the evening. That is the history of commuter. Must be affordable, must not have too much comfort, etc... But the core element is that you have sufficient airports in your range of around 400nm.
About the profits: Don't forget that the aircraft page only displays Earnings After Direct Costs (EADC). Your company's general costs are not included yet.