I'm glad you've never had a problem with it. But sometimes people do leave jobs rather than simply move to a new job on good terms. I couldn't imagine being forced to work in a job that I no longer wanted to work.
If something changes at work or in my personal life and I no longer want to work at my job, I have the right to say "goodbye", and leave immediately, and I wouldn't want it any other way.
If you've seen an American TV show where someone says "I quit!" and walks out the door, that isn't just a trope. I know people who have done that. As should be their right.
If an employer ceases to be professional, reasonable, or safe, there is not a damn thing wrong with immediate termination of employment from the employee’s end.
If an employer can terminate the agreement for just cause immediately, why can’t the employee?