I would agree with everyone, your home is probably priced too high for people to make an offer. In the time it has been on the market have you reduced the price at all? It probably depends on the feedback you're getting as well. Although if there was something glaring turning people off from the home, you'd know about it from that many showings. If you're getting pretty good feedback and something about the layout doesn't fit, or the yard doesn't work. It's probably the price or lack of price reductions during the 6 months it's been listed. If you've had none, buyers may see that as a reluctance to be willing to negotiate with them, and are making offers on other properties that they feel they can negotiate on price and/or inspection items.
Keller Williams Realty