I may be wrong but the reason is again privacy (and probably cost). If they tracked your queries and tied them back to you for future then they need to store your information or enough to tie to you and what you clicked on and the history to improve things. These all become things that they can be subpoenaed for which is anti-privacy.

Don't believe for a second that governments are not already banging at the door for access. The only ways to combat is either hosting in neutral offshore datacenter and incorporating there and living there is to not collect "useful" information in the first place on users. I think they went for the latter.