Its a gravity well, and missions there require not only getting there, but braking, matching speeds, landing on a specific spot on a planetary surface--and then all those problems in reverse when you decide to come home. Remember, in space, physical proximity isn't the issue. its how much propellant you need, and how long you have to wait for all the bodies to be in alignment.

To partially compensate for this, they'll put up a lunar orbiting station, so maneuvering and communication is partially simplified. But this now means we have TWO bases which will need support and maintenance, and twice as many things which can go wrong. An emergency on the orbiter not only threatens that facility, it immediately isolates the crew down on the ground.

What we really need is another ISS, in an orbit on the ecliptic optimized for launching planetary missions, and a facility designed as a spaceport, for assembling large spacecraft from smaller components, and staging multi-ship missions. A base at one on the Lagrangian points might be even better.

NASA has a penchant for very competently executing the wrong mission. Apollo, ISS, the Shuttle all proved to be expensive mistakes. Besides, he moon just isn't on the way to anywhere else.