Or to put this differently. If I was working for some larger company as a developer, and I went to management and said "I have decided that I want to quit development and work in marketing", they would turn me down. And rightly so, because A) it would be bad for the company to lose my development skills, and B) there is no reason to hire me as a marketing person when there's many more out there far more qualified and experienced in marketing.
So...if this would be quite clearly the correct course of action if I worked for someone else, why would I not follow the same thought process for my own company?