Some of the problems I see.
National pride has been the driver so far. That's wearing out.

Promises haven't been kept, the public is distrustful. The Space Shuttle delivered at best 10% of the promised return at 100 times the cost.

The ISS struggles to stay up there at tremendous cost. Very little worthwhile science. Many other projects abandoned to fund this boondoggle.

Mars Rovers have answered a few questions, it's been months since Curiousity hit the front page.

International tensions including a huge military preclude spending money on space. When we had it we gladly squandered it and now we don't have it.