Correct me if I’m wrong, but I believe you’re asking why different schools (Arts and Sciences, Lynch, CSOM) have the same major available in all three schools.
This is because different schools have different requirements. For example, most of the items listed under CSOM are actually concentrations. The requirements for concentrations are usually ~6 classes in a given subject. For MCAS, the major requirements are usually ~12 classes, and can sometimes be more than 15!
For this reason, BC separates them so that each school can have its own requirements . It’s best to consult the specific school advisors if you need help planning out what subjects you wish to study.