Don't Let It Go to Your Head!
Leadership roles get handed out for reasons that have nothing to do with leadership. Sometimes it comes down to who you know, or a family connection. Sometimes a diploma is the whole qualification. The military has complained for years about this exact thing: college graduates being turned into officers with barely any time in uniform. And even someone who worked their way up, who logged real hours on the floor, isn't guaranteed to lead well. The skill doesn't always come with the experience.
A title is not training. Plenty of people assume that the word supervisor on a door means they now understand how to run things, so they start making calls about the operation before they've figured out how it runs. The urge to prove they're in charge, that the decisions are theirs now, tends to come first.
Those early decisions usually rest on thin knowledge of the place. The people who actually do the work day to day often hold the deepest understanding of what functions and what falls apart. A new boss who feels shaky worries that asking those people for input will read as weakness. So instead of leaning on that experience, the insecure move is to start changing things, partly to look decisive, partly because the assumption is that the old way must have been broken or they wouldn't have been brought in to shake it up.
There's another motive underneath some of it: wanting to remind everyone who's running the show. Pushing through changes that are unpopular, which the newcomer has decided are necessary from a vantage point they haven't earned yet, is one way to send that message. The result can be tossing out things that worked fine right alongside the things that didn't.
Put people into these positions carefully. Learn what actually makes someone good at the job and how sound business decisions get made before handing over the authority to make them.