I don’t like to speculate as a matter of principle, but given what I’ve seen in my own evolution and what I can see traces of in some others, I suspect fear underlies a lot of it, as well as pride; fear of the implications of what it means and pride in not wanting to lose the idealized self image of western supremacy. If the US, for example, is genuinely terrible to the core on a fundamental state foundation level, that means a lot of pretty big change is necessary and change can be scary. And further, if a place like China or Vietnam is actually just a genuinely better system on a fundamental level and has better QOL for its people, that means the west is not only not superior, it’s not even on an equal level of political competency. Instead, it’s actually lower and in the capitalist caste socialization of “everything is a rung on a ladder,” that means the west is part of the “gross/bad class.”
People don’t have to see it this way though. They can see it as it’s not something to be afraid of, but a wakeup call that what’s being done is not working for most people and never has; they can consider the notion of major upheaval as an opportunity for fantastic expansion of the possibilities they’ve previously had presented to them, within which can carry drastic healing, improved quality of life, both personal and collective empowerment. They can also see the pride thing not as a designation of lesser nation, but as a designation of better or worse quality of life and empowerment and so on. It’s important that people unlearn the notions of it all being about caste, and who is and isn’t “superior.” Socialist projects doing better for their people are superior in the sense of quality of life, people power, etc., not in the sense of some colonizer-centric mindset of civil and savage.
There are some paranoid levels of thinking in some of that stuff. Like when a person thinks someone is a “x foreign country spy” because they disagree. It’s possible for people to break out of that mode of thinking, but when they are in that mode, it’s next to impossible to get through because everything you say that is in disagreement is “because you are trying to deceive them.”
Liberals claiming someone is doing whataboutism seems like a component of this thinking, with a belief that the one doing the “whataboutism” is attempting to deceive. But although it’s (probably? I haven’t analyzed it in enough depth to say with certainty) possible for someone to deceive in that way, it’s also possible to compare two things for a variety of rhetorical purposes that have nothing to do with dishonesty. Such as pointing out the US has the highest incarceration rate in the world if someone tries to say x foreign country is “authoritarian” in contrast to the US being “free”; that’s not whataboutism, it’s a factual point that undermines the narrative of the US having some kind of greater moral standing from which it can properly judge other countries.
If anything, I would say imperialists, liberals, tend to be more engaged in actual whataboutism, even if unconsciously. Like if you try to point out something fundamentally wrong with the US, claiming that alternatives are way worse. Which in that regard also seems to be in bed with doomerism (or more formally maybe, capitalist realism).