Why do so many Tea Partiers insist that they are NOT Republicans?

We all know they are- why insult peoples' intelligence? Saying the Tea Party isn't Republican is like saying NPR is fair and balanced- we all know they lean to the left so why keep up the charade? They could easily just say "We are Republicans who don't think the current Republican core is Conservative enough, so we have broken off." THAT would be believable. But pretending they are the modern day Whigs with no party affiliation seriously calls into question their credibility. Why the games?