Because if you change your registration you will not get a primary ballet for the R candidates. I registered as an independent about 20 years ago and realized I never received a primary ballet where the tea party has been able to purge the old guard. Its the primaries that have been easy to manipulate to stick it to the establishment. Just because I am registered R, doesn't mean I have to give them any money and every time they call I tell them that, "no money for you, my money is going to (fill in the blank) candidate as they more represent my interest than the R party."
Last night when the Gingrich organization called for support and money, I told them something I heard here, "why are you calling me for money, call the White House, they have all the money." The caller laughed.