Can someone tell me the advantages if any to an unelected cabinet?

Under a Westminster system, such as the UK, Canada, Australia, India etc etc etc, the cabinet, that is the executive of the nation is selected from the sitting members of the government. Usually they are selected from the Lower House (The Commons, The House of Representatives etc) but equally they can be selected from the Upper House (The Lords, The Senate etc). Admittedly in the UK a cabinet member selected from the Lords is not elected, but they are for practically every other Upper House member.

In the USA however, the cabinet is not selected from sitting members in either house of Congress, but chosen by the President himself from... anywhere really.

Doesn't this inherently lead to nepotism of the highest degree? Would it not lead say to the President picking someone who might have helped fund his presidential campaign? Is it possible for the President in theory to pick his brother, cousin or best friend for a cabinet post?

If the cabinet is unelected, then it follows that if the public didn't like them there isn't any recourse for them at all. At least in a Westminster system, the local constituents of the member can vote them out of their own seat at the next election - as was the case with John Howard at the last Australian election.

I'm afraid that I don't honestly see any benefit at all to having a cabinet that's unelected.