They've been doing seawater to fresh water conversions for a long time now. You just don't hear of it because you haven't been exposed to it.
The first thing you should know is that compared to getting fresh water from the ground table, a stream, or artesian well, making fresh water from salt water is expensive as a process. You do it when you don't have a choice in the matter of where the water comes from. When expense is not as important as the availability of water. The main methods for extracting fresh water are either vacuum or osmosis.
There is another method that has been used called the condenser method but it's not as popular a method as it is slower to obtain a volume of fresh water. The advantage of the condenser method is it doesn't need a water source to start with. It pulls the water out of the air.
No matter if you use the vacuum method with a heat source or if you use the osmosis method, chemicals and maintenance are involved. In the osmosis method, there is a further expense of the membranes that are essential to the conversion. They aren't cheap. One such unit I used to work on took 6 membranes for the unit and were to be changed out every 3 months. The chemicals are for back flushing to prevent a buildup of minerals found in the seawater. It's a must if you expect your water maker to continue to produce the same volume. Ignoring maintenance means that the water maker will make less and less water until it fails.