I think many people, especially in large and proud nations, don't like the idea of being a second class power to the United States. That's certainly what motivates Putin and Xi Jinping. There's nothing wrong with wanting to be the best, of course. I welcome competition.
Unfortunately though this frustration with not being the lone superpower drives people to focus solely on what the US is perceived to have done wrong while ignoring the tremendous amount of good the US has done and continues to do for the global international order. Therefore people develop a very skewed and biased understanding of the world.
Multipolarity means warfare and carnage on a scale much greater than anything we've seen in the period of global peace and stability we've seen since the US has been the superpower.