What happens if you're about to go on an assignment? TDY? To school? While in school? IOE?
Sometimes from the company's perspective it's just easy to say "thanks, don't bother coming in." It's not necessarily vindictive, just a reality of what's easier.
True story (late 1990's) - new hire finishes training, but not IOE. Gets a CJO from their #1 choice pending medical. Tells training manager. Manager says "you've already been transferred to your base. Contact the CP." CP says "don't bother showing up. Congratulations. We'll take you off the payroll."
Years ago someone gave two weeks notice because they'd had a class date with their first choice. Company #1 said "thanks, we'll just cancel your IOE so you don't have to bother showing up." Oops, flunked the medical at the new company. Original company, after assessing how the person's honesty cost them their first job, gave them their job back. If they had never given notice they'd never have lost their first job. They could have just 'no showed' like several guys had already. Instead they were honest and it cost them, until their CP reinstated them.
When you look in the mirror how do you feel good about yourself? Stiffing your employer by not giving notice? Or giving notice even if it puts you at some risk?