Usually it's because all the stuff you learned "on the job" isn't terribly useful to running a business, because tiny businesses and large companies operate so differently.

This is not the case where the "job" is basically an apprenticeship, such as lawyer or plumber or what-have-you.

Not the author, but in my experience at big(ish) corps: it will gather lots of people that want a safe job, people that want to do only one thing, or people that want predictability. None of these are bad things, just that they are different from startups.

Also compared to a startup there are a lot of departments so you will probably need to do few things outside your job or even interact with people doing unrelated stuff to your job.

Turns out almost all jobs, with the possible exception of commission-only sales, are nothing like owning a business at all.

For one thing, you're only covering a tiny part of the enterprise.

Another issue is you have a performance safety net. Most people coast through life, which is OK, but that's not good enough for running a company.

The most important problem though is that a job has a well-defined path, but in business you can never know what the "right" thing to do is until after you've done it and it either worked or didn't. Having a well-trod path you can follow is a million times easier than starting with nothing and making it all up as you go along.

To quote King George 3 in Hamilton: "it's so much harder when it's all your call."

I think the way to do it is to start a business, inevitably fail, and then just rinse and repeat until you finally figure it out. Easier said than done!