I know as much as is possible about this case. I was around when the Manson family was in their heyday and when the Tate-LaBianca murders happened. I wrote an extensive paper on this very subject in college, long before the internet. I actually had to go the library and spent hours heating up the microfiche machine.
When the Supreme Court and the California Supreme Court declared the death penalty unconstitutional, all sentences were changed to life imprisonment. All prisoners in the state of California, serving sentences of life imprisonment, unless deemed LWOP, are eligible for parole. They don't have to ask, they automatically come up for parole.
Leslie Van Houten has repeatedly said she understands the enormity of what she did and she feels deep remorse for what she did. I don't think she deserves to be let out, but that's just my opinion. So, every few years the state holds parole hearings, she appears before the board and parole is denied. The circle of life sort of thing. Until recently, before Mason said why bother, he came up for parole also.