How did this only occur to me just now?

Democrats ended the shutdown because it was impeding the attack on Venezuela and military operations generally, because troops were about to go unpaid. It's the best explanation for their seeming "cowardice" or "incompetence." I've seen speculation that it's about preserving the filibuster to hamstring a future democratic president (lol), and that might be a factor, but foreign policy and American militarism is likely at least as important and probably much more so. It's so obvious that I'm ashamed of myself for not thinking of it earlier.