Only bidder but bid rejected.

I had been watching a certain vehicle for a little over a week. It had been on 4 previous timed auctions and not sold in any of them. Today I sent someone to view the vehicle and after that I bid. I was the only bidder so I won the bid and then surprisingly I get a message that my bid was rejected. I call and they say I didn't reach reserve. Why would you put a price on something then turn around and say the price is low.