So what is the reason we buy these? Honest question... I really don't understand.

The B 21 raider is built by Northrop Grumman. Read my thread below to understand how the military industrial complex works…

It’s true that it’s a jobs program, but a massive investment in infrastructure and education would be even more of a jobs program. Plus the skill set that goes into the defense industry could be easily transitioned to peace building and peacetime projects.