So why is Bruce associated with "Dad Rock"? What does Dad Rock even mean?

On the one hand, I don't really disagree that he's considered Dad Rock. But I'm struggling to pinpoint "why" exactly.

I remember discussing with one of my friends about the definition of Dad Rock. And even among older artists, not every artist is considered "For dads." For instance, they didn't consider David Bowie or Queen to be Dad Rock though you could argue that the non-Freddie Mercury members of Queen have a dad vibe.

I know Billy Joel has occasionally been described as Mom Rock. The members of U2 have been described as Dad Rock, but not The Clash. I suppose there's a sort of dorky and silly quality that's associated with Dad Rock but I'm not sure.

How do you define Dad Rock, and Bruce's association with the label?