Is it really so surprising?
Most workplace are still built on the structure of the industrial revolution manufacturing plants and those plants , either we like to remember it or not, used a lot of children at the bottom of the ladder to do all the basic labor.
At that time being one of those kids and being a jerk or not following the rules didn’t get you a promotion… Grown ups had the higher jobs and naughty kids ended up as street urchin selling buttons.
While I totally agree with your logic and how there is a lot to gain to learn to be an adult at work, I do have a reserve on the benefits to “act” as an adult as the best thing to do in certain jobs/environment. Sometime acting as a good child (or a student) is the safest option at the time.
Maybe if learning to be a work adult was something everyone did as basic training even before heading to their first “career” job, then the workplace structure would evolve to treat (all) employees as adults and we could all move from there. I doubt the current structure would survive long if an overflow of “adult” worker started coming in not only at the top but even at the bottom of the structure.