Because most golf courses, esp so in drought prone areas are designed to maximize water storage and are already strictly rate limited on how much public water they can use. They also become safe havens for wildlife in metropolitan areas. TPC Las Vegas is a great example. The entire course was designed with industry best management practices using natural drainage areas to collect stormwater runoff into the various ponds and it is then used later for irrigation across the course. Most of the time they do not even need their allowable amount of city water. Golf course superintendents are some of the most conservation conscious people I know and are using best management practices not only to save the course money in irrigation costs, but it also creates a naturally beautiful landscape that wildlife enjoy and golfers want to experience. Some raw video I took from a commercial video project I shot there few years back.
