Why does every celebrity have to snob someone on Twitter?

They don't.

Realize that they are 유명인사 and there's not much time on their hands. If they respond to you, they have to respond to everybody else. And if that happened, with their popularity, they'd respond every 초 of their life tweeting without eating, sleeping, 또는 even going to the bathroom. LOL
Poor them, they'd be dead 의해 now.

Now if 당신 were a celebrity, 당신 couldn't respond to all tweets directed to you. It's too hectic.