The moon landing was pushed by Cold War politics (and funding). Those projects take huge amounts of money, and NASA had them. After that, the interest tapered off.
I don't think that's true. Well, it is true that there is less funding now. But it's also true that in nearly every industry, the overwhelming trend is to do more in absolute terms with less in relative terms. E.g. what percentage of the average person's annual income would it cost for a transatlantic flight in 1969 compared to 2009, and how many people do it? (That will have to be rhetorical for now as I can't find the numbers with a quick Google). Yet in 1969 (50 years after the first non-stop transatlantic flight) transatlantic travel, while expensive, was unremarkable. By now shuttle flights ought not to be an "event" but routine... And the first 747 flew in 1969, now you can buy 'em off the shelf.
There needs to be political will too. There are huge risks involved in taking on monumental projects. What if NASA spent billions of dollars developing a major project that fizzled? If there's no political power behind it, NASA risks losing all of the funding they get in the first place, and definitely not being able to get more to finish what they started. As an organization, it is safer to survive doing lots of small, achievable things, and wait for the day that the world-changing missions are an important political tool again.
