Not leaving sensitive equipment around for others to steal. Not cluttering up Near Earth Orbit with junk. Not sending back results over interceptable radio-wave

Not leaving sensitive equipment around for others to steal. Not cluttering up Near Earth Orbit with junk. Not sending back results over interceptable radio-waves (encryption can be broken, given enough time - if you broadcast it, you can pretty much assume that the bad guys will be able to read it in 10 years time) And then, I wouldn't be surprised if the military see this as a way to get a surreptitious military manned space program up and running - it's just not that much more work, once you have a lander available. That's just a few ideas that pop up at first glance - there are no doubt others...