The notion of 'experts' is changing, and now there are many of them, in the form of bloggers sharing their experience in class, for example.
Voluntary participation allows teachers to decide to what extent they want to be involved, how much work they want to do, etc.
They decided that organising things into career paths might be a more useful way of organising the information. For example, you want to develop your ability to teach teenagers or to write materials. You use the site as a scaffold to work towards your goal, through a series of challenges and goals and expertise to get you there. There may also be an element of gamification to help make it more interesting.