Each of these participants brings differing goals, requirements, and powers to the overall process. In the case I am most familiar with, the Japanese writers and publisher share a basic commitment to a liberal and individual-based society. In my case at least, the native English speaking writer was an integral part of the entire planning and writing process. Mombusho, the first audience, is concerned most directly with vetting proposed textbooks for linguistic matters. Their deliberations carry an implicit social management aspect.
Teachers are important because they are the purchasers of the text.
They select one text out of all those on the market because that text promises ease of use, seems topically interesting, and appears to be appropriate to the level of students they teach. The Japanese writers I work with consider students next. Their goals and requirements and interests and concerns are perceived indirectly, through the reports of teachers as communicated to the publisher. Their power is similarly attenuated. ALTs come last in the hierarchy of audiences.