By your logic, the flight school I'm currently attending should have one helicopter per student/instructor pair since we could get more flying done without having to schedule helicopters. From the point of view of the instructor and student this is a fantastic idea. From a business standpoint it really doesn't make much sense. They do, however, give each student their own headset and view-limiting devices. We could share those, too, they're only used when the helicopter is used.

Can you think of reasons why maybe each student doesn't have their own helicopter but does have their own headset (assuming they were cleaned properly after each use and hygiene wasn't a concern)? Those same reasons apply to the office/keyboard situation.