When there is an actual cost to Zuckerberg's behavior. So far, Silicon Valley is fine working for Facebook and Wall Street fine financing it. Users aren't rebelling. Advertisers are docile.
Where is a politician aspiring to take Zuckerberg on supposed to find berth? (Genuine question.) The only fecund ground, to my sense, is the far right accusing Facebook of censoring its Nazism and far left upset that Zuckerberg is rich. Neither makes for a sustainably extensible base.
If it wasn't facebook it would be tv, magazines, or something else. I find it exhausting how people blame facebook for being a reflection of societies ailments as opposed to trying to solve the underlying ailments.
However, if there is a legally permitted action that Facebook can take to protect him personally, and only Facebook can take it, I don't see the problem with them deciding to do so.
If Zuckerberg is accused of a crime as a private citizen, he is of course capable of paying for his own defense. These are the examples you gave but they do not reflect the situation here. The story here is that the FTC wanted Facebook to pay a $5B fine. Not that they made Zuckerberg pay a $5B fine and Facebook decided to reimburse him for the expense.
The story here is that Zuck was going to be accused of a crime as a private citizen, until FB decided to up its settlement offer from 100 million to 5 billion.
Stealing's a crime; breaking contracts between FB and the FTC is not.