Just like having a pre-nuptial agreement. It's a common practice to have an NDA when famous people enter relationships. Donald Trump had his fixer Michael Cohen, NDA his lovers - Stormy Daniels and Karen McDougal, once he decided to run for the US presidency.
In my professional life, working in tech, mutual NDAs are used when companies need to collaborate with each other to ensure that there is no un-authorised disclosures about the collaboration.
If I was a person of high net worth, then I would ask employees (people I pay) to sign an NDA to ensure that I had recourse if the employee revealed family information without my permission.
NDAs are not always a bad thing.
It's known in the entertainment industry that various "people" enter relationships to publicise their commercial interests. Imagine if say Diane Buswell and Joe Suggs had such a relationship - I think they are a true partnership but one could imagine a couple similar to them engaging in such practices. It allows one to engage in the relationship secure in the knowledge that they'd have some redress if the other party disclosed stuff without the first party's consent.
A few years ago in "Private Eye" they talked about Elton John having such an NDA with his former wife Renata Blauel - if either party talked about the relationship then the other party was entitled to a substantial sum. The aim was to silence Renata. About 10 years ago Elton John published an autobiography which mentioned his marriage with Renata - he didn't say much about it, but obviously he had forgotten about the agreement with Renata and had said enough for her to enforce her side of the NDA. The whole thing went to court and in the end (about 2016) Renata won and got her money. Private Eye's angle on was that it served Elton John just right being the target of a breach of privacy law/NDA suit after initiating so many himself.
Here's a report on the case from "The Guardian"
https://www.theguardian.com/music/2020/oct/14/elton-john-and-ex-wife-renate-blauel-settle-legal-dispute#:~:text=Blauel sued John for “repeated,her connection to the singer and more details of how Blauel had tried to keep to her side of the deal
https://www.theguardian.com/music/2...-identity-to-shed-links-to-singer-court-hears
I can imagine Skanky has learned that an NDA keeps her safe if she has an ongoing thing with some "egg" and that's why she NDAs her boyrfriends.