There are several reasons...sometimes, as already stated, the seller(s) are not motivated for what ever reason. Sometimes, they want to make sure the home is perfect for every showing and if they can't scrub and clean, they won't show the home. Sometimes their agent has not fully explained the importance of showing, whenever another agent or client calls.
My question for you is: Have you attempted to see these homes and been denied? Were you just checking them out, or are you a serious buyer (pre qualified and ready to go)?
I've had listing where the sellers specified agents and/or individuals they did not want in their home. To speculate that it has something to do with possible foreclosure seems to me to be out of left field and, quite frankly, not your concern. While a sellers motivation is nice to know, it's not generally shared by listing agents.
Keller Williams Atlantic Shore