One problem is that people may have algae growing on their water, or have discoloration (green water, or cloudy). There may also be issues with the water smelling like chlorine, or problems getting the pH balance correct. Additionally, some people have issues with the water burning their eyes.
Pools require a lot of maintainance. You have to put chemicals in regularly, as well as keep it clean. Those both cost a good portion of money. Also, the chemicals have to be well balanced.