I think that some folk write down what they find in the classifieds, fully intending to write an e-mail "soon" to ask about the item for sale, and then procrastinate for a long time before actually getting around to writing to the seller and do not re-check the classifieds to see if something is still available at that time.
Then again, some folk don't actually READ, but see the photo or title and jump to the conclusion that if it is still there it must still be for sale.
But, I would expect that if the seller is still being contacted that they should realize the advert should go away now.
I once responded to a newspaper ad from a fellow that was buying trains. I was in dire financial straights and decided to sell my old Lionel train set (ouch, oww, ouch, oow... I'm still KICKING myself for doing that!). I called him, he came to see it and we agreed on a price and it was gone. I was sad, but my family could eat.
I continued to get calls from him every couple of months for over two years because he had written down that I had a Lionel train set for sale and he wanted to know if it was still available. In that two years I got back on my feet financially and tried to buy it back from him... he never called me again.
As for the Search button... yes, I sometimes wish folk would use it a bit more, but there are still folk out there that are new to the internet and forums and have no idea that a search function or an FAQ exist or even know what FAQ means (Free Action Quote?) so they don't know to look for one. Then there is the mental block of what key words to search for and the fear of being inundated with irrelevant information that would take too long to wade through or missing the one piece of information that is relevant because they used the wrong search terms... so they just ASK for the answer instead of LOOKing for the answer.
And then, sometimes, asking again can bring out another viewpoint that is worth considering and makes the repeated question a worthwhile thing.