Why is an orgasm after busting so much more intense

I've only ever done self busting (sadly haven't found someone to bust me... but I hope that doesn't make this against the community rules due to being self rather than F/M, if it does I'll be willing to delete the post) and I USUALLY don't hear about this side of things but does anyone have an actual explanation as to why it happens? Is it only because I enjoy ballbusting or is it something the male body does (like is it a way for the balls to try to get seed out in case of injury or something)?
I just did 80 average strength self hits and ropes after where as since I've been away from busting myself (for about 2-3 months now) it's usually a dribble.