Because they're so used to hierarchy based on oppression, pedigree and greed rather than contextual hierarchy based on actual merit and expertise.
I'd rather take orders about plumbing from a plumber rather than orders from a guy who bought a plumbing company but never did plumbing in his life.
We are all very used to the latter. We have people making public health policy who believe in homeopathy. We have car building companies run by guys who have never built a car. We have guys in control of armies who don't know the literal definition of genocide. People in charge of companies that make food that have never had to take a single class on human nutrition.
Of course people are going to be allergic to hierarchy when we're so used to the people in control being unfit for their role.
Hierarchy is a lot different when instead of a single dude being in power because he's a rich asshole, it's instead deferring to someone who has more expertise in the task at hand. Hierarchy doesn't have to be rigid either. The guy who you're deferring to about plumbing might suddenly have to defer to your experience in electrical work.
True, contextual hierarchy that is based around what needs to be done and who is trained to perform the task and can adapt based on what kind of skills are required isn't bad.
Like, I'm going to let a surgeon be the boss of me when it comes to surgery.
I think the 'self enforcement' approach to covid is a good example of why sometimes you do actually need to give authority to save lives. The important part is getting right who you give authority to. Right now we give it to the least qualified and most bloodthirsty people.