One problem is that so many newcomers to the profession - particularly those living with family, start out doing Outcalls only while they "test the water" and get a few regular customers, and don`t do Incalls until they are sure they are going to make money. When this happens they start doing Incalls, and it suddenly becomes too expensive, too time consuming, or simply too much bother, to travel for Outcalls.
I have had three regulars who have started this way, and all eventually reaching the stage where they become reluctant to bother travelling, either at all, or except at much higher rates.