Why hasn't mankind outdone itself in over 40 years?

I am of course referring to the Moon landing in 1969. It was mankind's greatest achievement. Why no lunar colony, or humans sent to Mars? Did mankind just give up? Did they say: "well we set foot on another world, we gave this whole space exploration thing a shot, that's that"? Sure, the rovers and the telescopes are great, but can't mankind do so much better? Can't we outdo ourselves, and do one single achievement that blows all prior achievements out of the water?