They do it for the same reason that people went to see Elvis Presley in Las Vegas around 1974. They have an image in their heads of an older better Rockefeller who's been long dead. It's the same reason everybody loves the Kennedys.
Personally, I'd have to go with the '74 Elvis. [irony]
The clock is ticking on the Kennedys as American royalty.
Let's review: Jackie's dead, John-John's dead, Maria Shriver is more Mrs. Schwarzenegger than Jackie's niece, Eunice Shriver, who has those durable genes her sister Rose had, looks like Norman Bates' mother in Psycho (I'm not being cruel -- Google a recent photo), Kathleen Kennedy Townsend got bounced in Maryland by Robert Ehrlich (and the MD4BUSH scandal can't be good for Demos in the state, including her), Robert Jr. is an envirowacko Chicken Little trying to make us forget he became a junkie, his brother Michael died skiing into a tree (after ruining his rep messing around with an underage babysitter), his cousin and RFK Sr.'s widow's nephew Michael Skakel was convicted of murdering a teenage girl a quarter-century after the crime, and Mary Jo Kopechne sacrificed her life to ensure Ted Kennedy would never be Commander-in-Chief.
I'd say the bloom is off the Kennedy rose (pun not intended).