Because it’s pretty dumb to make yourself jobless if you don’t have another job for you to jump into right after you quit or give your 2 weeks.

You can only do that if you’re well off enough to quit & take a few weeks to job search while still being able to pay your bills.

You owe your current job nothing if you want to find elsewhere to work. Using them for money until you find another job is the smartest thing to do.