Beerus might make fun of his brother and his liking to wear diapers but he has a crinkly secret of his own. He wears then just as much as Champa does, but he actually needs them. Whis just hides the fact he wears them from Champa by using his powers to hide the crinkle, the bulk and really any evidence he's wearing them.
It started a couple hundred years ago when he and Whis flew too close to an electrical storm in space and Beerus got zapped pretty bad. He felt fine afterwards but it didn't take long for his bladder control to do downhill. Eventually after so many pants wettings right outside the bathroom Whis just got tired of cleaning it up and got poor Beerus some protection for his problem. He resisted at first but eventually begrudgingly accepted them as something he very much needed. That doesn't mean he has to like it at all though and whenever Whis changes him he groans in humiliation at the fact of being a destroyer god in diapers. Whis always knows just what to say though to make him feel better about himself though.