Oh I'd say NDA's are a must and that it's completely normal in the biz. But what exactly KP is hiding with hers is anyones guess. She probably tells them in the beginning its to stop them selling stories on her, giving them the sob stories of her past and then once they're fully indoctrinated and work out what's going on its too late.
I think she must come across as quite vulnerable in the beginning and love bombs them like a pro, and foolishly they get sucked in and may even have some type of saviour complex. Lets face it shes had enough practice at early days relationships and has honed her skills to perfection that I don't think these idiots know whats hit them when they finally cop on, some stick around for the fame and perks but they all get out eventually.
Shes not exactly the personification of hotel california or maybe she is?