The pollsters aren't asking about them:
My New Hampshire phone rings (caller ID 000-000-0000 WTF?)and I pick it up out of curiosity. "This is (talking like a magpie so I haven't got a clue what the name of the company is) Research. Would you like to be part of a poll for the Democratic presidential primary candidate?" I agree and the woman rapidly reads the list of candidates. "Clinton, Obama, Edwards, Dodd, Biden and Richardson." I say, "Kucinich." The woman on the phone says "Who?" I say, "Kucinich. Dennis Kucinich." I hear coaching in the background - apparently the call is being monitored. "I'm sorry, but Dennis Kucinich is not on our list. Is there anyone on the list I gave you who you would vote for?"
So there you have it. Kucinich is down in the polls because he isn't included in the polls . . . and you can forget about Gravel, too.