managers are worst-case analyzers

There are a lot of difficult decisions to be made in life. Maybe you need to decide the business strategy of a company, knowing that good strategy matters and that you have thousands of people's livelihoods and maybe billions of dollars of humanity's capital riding on your decisions.

In making these decisions, sometimes you need to be able to say, 'this is the best we can do'.

As an individual contributor, you have a 'there exists' quantifier on what's possible. You know certain techniques and have some things you can do.

But as a manager, you need to have a 'for all' quantifier on what's possible. You need to be well-connected enough that you can ask the right people, and if none of them know how to do something, you can reasonably conclude that it's not possible. An IC would never be able to say that something's not possible, because with enough ingenuity anything is possible, and an IC's job is to find that ingenuity. But a manager needs to make immediate decisions, which means having a narrower sense of the possible.

Counterpoint: managers can also think bigger than individual contributors. They can invest in projects at large scope with ambitions that would seem impossible to an individual.