These keys aren't exactly hidden. This is like trying the doorknob a second time.

In determining whether keys-in-locks or keys-under-doormats is the closer analogy, I have to go with the doormats. Various people go door-to-door... delivery people, campaign volunteers, Jehovah's Witnesses, etc. and a key in the lock would be hard to miss. A key under a doormat is easy to miss, being obscure. Sure -- the doormat is one of the first places you look if you're actually trying to break in, but people whose nefarious side doesn't manifest until the opportunity is obvious are indeed thwarted by that obscurity.