It's possible that people can actually be former leftists/socialists/communists/etc and have "left the left" so to speak. I've been noticing here that the common response to this will be "they were never really leftists/socialists/etc. anyways" or "they were never really serious to begin with." It's possible that it could be the case, or maybe they actually were on the left, but they just didn't have the stomach for the real shit I guess.
I think we shouldn't be too quick to jump to using the "no true scotsman" fallacy in these cases. For those who don't know, it's basically saying "you weren't REALLY a leftist, cuz otherwise you never would have left." The same argument is used by religious people when someone leaves the faith: "oh they were never a REAL christian, otherwise they wouldn't have become atheist/agnostic."
To give some concrete examples, take Eldridge Cleaver. He actually was a Black Panther, radical, communist, etc. but then later in life became a Reagan conservative. Or Angela Davis. She actually was a radical but now she tells people to vote for Biden.
TL;DR: People can and do change, sometimes for the better, sometimes for the worse.
I rarely see anybody coming for Angela Davis-like figures and questioning their authenticity. But when somebody like Dave Rubin makes a big pageant about "why I left the left" as a stepping stone to their new conservative media career, you have to at least wonder if they're being cynical little liars.
That said, there is no way to literally read their mind. Maybe the money clouds their judgment and they actually convince themselves.