I do it for the same reason any other professional would. To offer a better quality product and experience in an area I have a natural ability for and interest in. Over the years, I’ve tried my hand and other genres of photography and keep finding myself coming back to three very distinct areas. Weddings, seniors, and commercial work. I love all three specialties and I have worked hard in each area to improve my skills to a level where I can say that I specialize in each.
Just like with a generalist in any field, you can get a "good enough" product and maybe even a better price. But, when you really want a job done well you ask to see someone who specializes. Why settle for good enough when you can have something great? A specialist doen't miss a moment, knows how to light and pose to flatter their subjects, and how to help you showcase your own strengths and your story. You never get a second chance to photograph your wedding day, you only graduate from high school once, and you have only moments to make a first impression. Why risk any of these opportunities in life on a cheaper alternative?