Usually, if it's been around for a while, the owner's run out of time and/or patience.
Often happens when they bought before selling, building and they need to finalise now to move etc.
Can be an opportunity.....
Often happens as property was overvalued in the first place, or couldn't agree on terms. (ie got the price, but dont want to settle fast and have to move/rent/move etc)
Can be a good time (if you like the property) to talk directly to the vendor and find out expectations, or put in a pre-auction bid.
Cheerio
Simon.