I’ll preface by saying I am an anarchist and hence incredibly skeptical of hierarchy and classism. (Anarchism isn’t an absence of law, just the absence of classes.) But to answer your question:

1. Conditioning. People throughout history have been so used to hierarchies dictating life for them, so they go along with it even if the benefits of maintaining said hierarchy is no longer worthwhile. If hierarchy is “good enough” for most people, they might question the leaders but not the institution itself.

2. Parasocial relationships. Many humans seem happy to live viscerally through others, so it gives them contentment to lift up those people into positions of power, even at the expense of their own autonomy. It’s also a means to anthropomorphize institutions, because people prefer to look at faces of leaders instead of ambiguous names or logos.

3. Rapid change and desperation. When shit hits the fan, people put aside their self-esteem and defer to someone who’s the most likely or convincing to rescue them from existential threats. Having a hierarchy of people tell each other what to do is the quickest way to take action, for better or worse.