This is strictly about things a person needs to do for their own financial and employment future after leaving. There's nothing here about handing off the job responsibilities and knowledge to colleagues, for example.
If you DGAF about that, you might as well give no notice.
Employees give two weeks to be nice and not burn bridges with people on their team.
Employees who are angry at their employers may often give no notice at all.
Employers don’t give notice in layoffs because disgruntled employees are not productive and are a liability.
Employers don’t give notice in terminations because they don’t want them working for two more weeks.