The problem is that Congress wants to have their cake and eat it too.
They want to have the benefits of UN and NATO without any of the drawbacks. They want to have the benefits of military pork without any of its drawbacks, either.
So, rather than do the difficult yet legal, Constitutional thing and terminate treaties or hold up spending, they prefer instead the illegal, unconstitutional yet easy route of picking and choosing when the President is allowed to be the executive and how.
Consider, though, Article I, Section 8 “The Congress shall have the Power To: ... make Rules for the Government and Regulation of the land and naval forces” clause. I’m not so sure the “unconstitutionality” of the War Powers Act is so cut-and-dried. The Founders were opposed to standing armies and certainly to the Chief Executive as King. The Continental Congress wasn’t hands-off when it came to the Revolution. I think a framer’s analysis of the WPA would find it to be a very good balancing of powers while permitting the CiC to act in extremis in defense of the Nation.
Essentially, what Congress wants is the pretense of power, but with sufficient insulation from responsibility to be able to convincingly blame failure - or disaster - on someone else, without ever having to explain themselves. Profiles in courage they are not.