Because Bark (Brozone's Dad) Is A Pop/Rock Troll Hybrid. He Inherited Some Of His Dad's Features. Like his Pointed Ears and Sharp Teeth. He Could also see in the dark.
Bark Was Often Bullied By Some Other Pop Troll Kids For His Looks. They Would also Make fun of Him For Having A "Weird Dad" (Not All Pop Trolls Are Nice. We've Learned That From Creek) He Was so ashamed of His looks, he would wear Big Headphones to hide his ears, and A Face Mask to hide his teeth whenever he went outside.
Despite this... Bark Held NO Resentment Towards his Dad (Thorn) He Still loved and cared for his Father, despite the fact he was A Rock Troll... But sometimes Bark still Wished he hadn't gotten any of his Dad's features. His Mom (Rosiepuff) would always try to tell him that his unique features make him beautiful... But that Sadly didn't stop him from being bullied.
Bark was very happy that he met his Wife Dandelion. She never said anything mean about his appearance, or Questioned why his dad Looked so different from the other Trolls. When they had their first Child John Dory, Bark was relieved that he looked more like A Pop Troll than he did. Bark Didn't want his kids to go through the same things he did.