Why do most moms or dads get upset when people say their baby looks more like the dad?

My cousin bluntly posted yesterday, “I’m just going to be straightforward, I am so tired of y’all saying mommy baby looks her daddy so I will PROVE that she has mama in her blood. Just love my baby.”
Damn okay…. It isn’t the baby’s fault. Mom are so straightforward and blunt and my cousin didn’t apologize for the way she was acting.