Why do babies have gas?

You would think that since babies are so small, that the little (or much)that they take in, it would be easier for them to burp. It seems that my pat,pat, pats that I give to Jack's back triggers an alert for him not to burp but to sleep. I can pat his back for what seems like a half an hour and nothing still comes out. That is when I pray to the Gods above to help me and have him let out a big buuuuuuuuuuuuuuuuurrrrrppppppppppppppp!!!!!!!!!!!!!!!!!. Miraculously, it works.