I thought most game devs were into the paradigm of: check external libraries straight into your source control, update them never, and generally treat them on p

I thought most game devs were into the paradigm of: check external libraries straight into your source control, update them never, and generally treat them on par with your own code. What is it that a package manager does that's particularly useful for game dev? (I don't do game dev, so maybe I'm missing something.)