I agree that understanding legacy code and code by other people is part of the job, but I don't see how these points are related.

> What happens if the person who wrote the code went on vacation?

They get yelled at, because shipping code at 5 pm on Friday and then leaving for vacation is typically considered a "dick move".

> What happens if the code is many years old and no current team member has touched the code?

Then the issue probably isn't caused by a recent deployment?