rebdoniel: Many people who do things like that either a) are only getting used to the idea of lending out their house (which, you’ll admit, can be pretty personal and invasive, to imagine someone else living in YOUR house using all of YOUR stuff, especially when you’ve never done it before) or b) have gotten burned in the past.
I’ve been in both places (in order, obviously) and I completely get why someone would lock certain rooms- in some cases it’s not so much suspicion as practical certainty.