Tentacles:
It's a weird term men are not the ones that have to go through pregnancy It's the women who have to go through the body changes.
That's not why they are called dad bods. Just as women face body changes when they are mothers (even if they were never pregnant), men face them too. This is because parents often neglect themselves a bit when they are focused on raising their kids.
Suddenly, you have less time to work out, and you find yourself eating more junk because it's quick and easy. So, naturally, a lot of people put on a few.
Not every dad will have a dad bod, and not everyone with a dad bod is a dad. But, it is most closely associated with a stereotypical father's bod. Hence the name