It is important, even very important, to realize that this merely changes the laws of economics to which they are subject, at least as people generally imagine them. It does not immunize them against the laws of economics. It does not mean they can just do anything without consequence, or with the full power to select the consequences.

This is in the class of "things that sound obvious when I say them", but I can see that a lot of people seem to throw an exception here and terminate all execution. Having negative equity matters, even if you can print money. It just may matter differently.

"or am I totally misunderstanding something?"

I would say, you're not so much "misunderstanding" something as not realizing that there's a whole complex of interacting systems hiding behind your "but they can just print money" that needs understanding. Whether those systems are deliberately obscured is a matter of some debate, but they certainly don't go out of their way to educate you about these systems. Everything is far more complicated and interconnected then you appear to be seeing.