As a matter of fact the latest Orbiter is missing a Space Shuttle that can simulate at least some of the basic maneuvers/tasks. The Fleet was far from being a replica of the real thing but at least offered some nice features specifically developed for a space shuttle (like GPCMFD, RPOPMFD, ORBTGTMFD, etc.)
My question is: can Orbiter afford to live with no "usable" Space Shuttle? Would you imagine a F1 simulator/game with no Ferrari?
A somewhat outside perspective:
This whole argument hinges on the definition of 'usable'. I've used stock Atlantis for a complete mission to ISS including re-entry with stock instrumentation. So it can be used to simulate basic maneuvering.
Is it particularly realistic? No, certainly not. But then it depends on the question of what defines realism for you. The real Shuttle has its idiosyncracies, like it is yaw-unstable over most of the aerodynamical range and needs to be managed carefully by the aerojet DAP. Is any entry realistic till you actually have a simulated flight controller taming the instability? Till you actually need to take care of vehicle trim before doing the entry?
I come from a flightsim environment where it's commonly acknowledged that instruments never show simulated 'truth' but that, say, an altimeter is driven by a simulation of pitot tubes with ram and ambient pressure and reacts to simulated pressures, not simulated altitude. Is anything realistic before instruments actually do it?
You're drawing a particular line between realism and complexity and say 'that's what I like to have'. Well - that's your personal preference, nothing more, nothing less. It's different for others, and this does not equal 'without usable Shuttle' - people who enjoy a higher degree of complexity and realism might find your preference unusable and find SSU very usable.
It would also be well to remember you're getting something for free here - you're not a paying customer who can demand certain services perfectly tailored to your liking.
Otherwise, if it doesn't come with a free software license, your only option is to get permission by the author. And there asking nicely for permission has a much higher chance of success than finger-pointing and complaining.
And, as others have said, if you don't like that, you'd best stay away from closed source software, because this is how it works - the author decides everything, and like any other license, this ought to be respected. Because someone did a lot of work and made it available for free.