You're in sales at a company in a highly competitive space and are exited. You're not the kind of person to premeditate taking anything with you, perhaps you left on good terms. You join another company and someone there asks you for the book of business or sales leads you were working on that the previous company. Oh look, your login to the CRM system is still working, and you can get a glimpse of information that you shouldn't have access to as a non-FTE. It seems benign, so you copy down a few phone numbers and email addresses. This isn't an academic example.

This wouldn't even be a possibility if the account was locked down immediately. It's obviously much more difficult to control access to information while you are employed (this is a subplot of Snowcrash, afterall), but immediate lockout isn't meant to mitigate that risk. It's meant to mitigate risks from an account being active that shouldn't be.