Returned or erased data?
At the end of contract period.
Hands up those of you who would be perfectly fine with the workman to whom you had lent a key to your house (to expedite repairs) making a copy of said key without your knowledge and consent?
Those with hands up, does your view change when you find out said workman has been convicted of multiple burglaries?
The difficulty of enforcing such contracts meaningfully, when oversight is in the hands of the very officials who picked the vendor, is a pretty high bar.
Not to pick on Palantir. They are far from alone.