Because I believe in the traditional way. The traditional way says that the instructor-student relationship is like the parent-child relationship. By this I mean that my job as instructor is much more than just showing a student techniques. It is to guide the student in their overall development as student and person. That is a primary difference between traditional and mixed martial artists. MMA see their instructor as simply a coach, one who shows them the required techniques to get the job done. In that aspect, you can learn from as many instructors as you want, because all they are doing is coaching in different techniques.
My perception of an instructor is much deeper, as is most traditional stylists. Learning technique is simply the beginning. Your instructor is almost a mother/father figure. How many fathers can you have? One. Many uncles but one father, the person who is responsible for your ultimate growth. Not only do they teach you their technique, but you also grow under their rules and philosophy. MMA undoubtably see this as stifling. Traditionalists see it as providing a firm foundation.