Because the budget law (authorization to spend money) and the tax laws (authorization to take money) are different laws. Lack of does not imply lack of the other.
In the absence of a budget law, the State has no (limited?) legal authority to spend money ... so spending money would be a violation of the law.
We can hope, pray, that our various governments would be so careful about obeying the law in other areas as well. Like, say, the limits on government size and power established in the Constitution.
“We can hope, pray, that our various governments would be so careful about obeying the law in other areas as well”
good point