Because they didn't want her to look scary with a horn coming out of her nose and forehead? That's why Barney doesn't have razor-sharp teeth and claws coming out of his hands and feet. It's a show aimed for toddlers.
And in that matter, how could B.J. and Riff be related to Baby Bop? They're clearly different species.
Help me out with the timeline. In many viewings of the show when I was a little boy, I've seen Baby Bop and B.J. be child-size, then adult-size. What is going on here? Is time somehow passing for them, yet not affecting the other kids and Barney?
BJ and Baby Bop both started out adult size, but shrunk in order to fit the character's ages better (seven and three, respectively). As for the interspecies dinosaur family thing, one can assume that BJ, Baby Bop, and/or Riff were adopted in a sense. Luckily, Barney doesn't have a family relationship to work with (in context, his friends are his family, as they bring him to life).
"Barney is a dinosaur from our imagination" that's how the theme song starts out. I think that clears up all your questions.
Personally, I've always thought of Barney as a Tyrannosaurus, B.J. and Baby Bop as Protoceratops and Riff as Saurolophus.
Word Of God says that Baby Bop is a Triceratops, B.J. a Protoceratops, and Riff's a Hadrosaur.
Maybe I'm making this up, but wasn't there a time where Barney had these monstrously huge, human-like feet before they decided to shrink it to the size they are now? I remember seeing a Barney movie as a toddler, and seeing those feet creeped me out. Did they actually have something like this, or am I just making it up?
Confirmed. Definitely changed the feet size there.
Why do people hate the show so much? A lot of people say it's because Barney looks creepy and he's always smiling. In that case, why isn't Big Bird or Mickey Mouse hated as bad? That never made sense to me.
The incredibly annoying voice might have something to do with it.