The government is currently $36 trillion in debt with that debt growing at an exponential rate. Our annual expenditure of interest on the debt has exceeded $1 trillion per year and will soon exceed the entire discretionary budget of the US.
And this is happening as growth starts to slow and other countries continue to reduce both their reserves and dependency upon the dollar.
Many don't see this as sustainable, or really even remotely sustainable. And so working to create more sound governance and spending today is motivated precisely by an effort to prevent a catastrophic crash.
Like think about to back before the housing crash. There were numerous shows on TV about people getting a house (often with near 0 deposit), adding granite counter tops, and then reselling it within weeks for a $20k+ profit.
Anybody could see that that sort of economic system could not possibly be stable, but most people have this instinct that a status quo must inherently be stable, but that's just not true. That unstable things have not crashed today is hardly an argument against them crashing tomorrow.