It's yet another way that the art world repeatedly slits its own throat.
Sorry about that graphic analogy, but it's true.  Let's begin by defining the term, "government."  The government is a conglomeration of individuals, many of whom are elected by the people, to serve the people and the best interests - let's hope - of the nation.
When you break everything down to its most essential elements, you're left with "people."  Someone has to make the actual decisions and someone has to do the actual work.  That would be ... the people.
And so, for all of this decades-long debate about government support of the arts, we're no farther along than when the debate began so long ago.
Why is government support for art so tough ... to get?
I won't claim that there's only one reason.  Nor is there a silver bullet solution.  However, here's a BIG contributing factor...
Why does the art world want people (a.k.a the government)  to support it when it works SO HARD to be exclusionary?  Why should people support such an enterprise?  It just doesn't make sense.
What's worse is the fact that most legislators - local, state or federal - don't know squat about art and even those who do are overwhelmed by other priorities like ... I don't know ... roads, schools, police and fire, water treatment plants, NATIONAL DEFENSE and so on.
I don't know.  Which is more important ...  paved roads or a contemporary art museum?  I want both.  In order to get both, you must be a diplomat and taking Psychology 101 helps tremendously.
In short, we can't have it both ways guys.  The art world cannot continue to operate as an eccentric, exclusive club if it's seeking public support.  Most people don't like snobs, nor do they approve of those who take their money and then create things that are poorly designed and engineered or worse yet, weird.  That's how so many people choose to view contemporary art.  It's their way of licking their wounds after getting snubbed by some art dealer's stuck up assistant.  It's usually those on the lower rungs who cop the most attitude.
If you're a contemporary art museum seeking government funding, you'd better be the nicest, most accessible, most gifted and insightful enterprise this side of the Atlantic ... or the Pacific for that matter.  And you'd better deliver on what you promise.
I'll say it again ... how many times have you ventured inside an art museum, gallery or institution and felt like you were on the verge of getting snubbed?  How many times have you actually BEEN snubbed?  More than once?  Yeah, I thought so.  I've visited some of these places with art world friends and we have found ourselves in this same situation.  It's just dumb.  The time spent snubbing potential patrons could be better used explaining art to the very people who might be in a position to award a grant.  You never know.

In short, don't we want to see art thrive rather than needlessly stuggle due to shortsightedness and lack of vision, if not flat out rudeness?  You don't have to be Einstein to figure this out.  
Why is government support for art so tough?  I can certainly give you ONE reason.   And believe me, it's a WHOPPER.