That's true if the project manager's personal and organizational incentives are to make estimates that are as accurate as possible.

For some people and organizations, the purpose of estimates is not primarily informational.

It's one of the many tools in the efficient tyrannical manager's toolbox, with a motto of "my goal is not to have you do effective work, my aim is to advance my goals and keep everyone below as a non-threat to those goals". Keep em busy and insecure.

Sure nice it doesn't work on competent developers, not with the current job market.