Every other country I can think of has a system where if the finance is not agreed, the previous budget just continues. The budget sets the yearly amount for each department and it runs on until another budget changes how much everyone gets. Sometimes a new department gets created, sometimes something is abolished. Everyone gets their salary and services run on. Even if the finance bill is defeated, or even if they can't agree a government at all.
So how is it so easy for the US to simply run out? It naively seems like something both sides would want to fix pretty quickly. Is there some unseen advantage doing it this way? From news reports it seems to be all downside.
Edit: Thanks for the enlightenment!