Twenty years ago, a woman conveyed land to a city so long as the city used the land "for park purposes." The deed was promptly recorded.Seventeen years ago, the city discontinued using the land as a park. Because the city needed additional parking for nearby city buildings, it paved the land and has used it as a parking lot ever since.The period of time to acquire title by adverse possession in the jurisdiction is 10 years. Last year, the woman died intestate, leaving a son as her only heir. The son sued the city, claiming ownership of the land, but the court found against him.What is the most likely explanation for the court's decision?