Is it bad that when my older brother has the baby he doesn’t even pay her any attention?

My brother has a baby by a girl who he doesn’t live with. He still lives with me and our mom. he’s 28 years old. When the baby is here, our mom takes care of it. Like feeds her, changes her diaper, rocks her, has her laying by her, even has her crib in her room. Our brother stays in the basement the *entire* time. Even when the baby’s crying our mom takes care of it. The baby’s 2 months old. It’s not like my brother isn’t here most of the time, he is. And the baby is here from Mon thru fri. I mean is this normal of new fathers or what? My mom even made remarks about how she knows he’s probably going to want her to take care of it on the day the child was born. My mom even buys most of the baby’s diapers and stuff.