I think many of us working in software can be overconfident about how easy it is to scale things, probably because of the peculiar progress in the improvement of integrated circuits and the commensurate increased availability of raw compute for not that much more energy. But many processes (including desalinization, as far as I understand it) are energy bound. It is really hard to make exponential progress when a process is bound by how much energy you can muster up to put into it. That is why rockets haven't had an exponential increase in the amount of weight they can get into orbit in the last 100 years. With gravity you must pay the piper.

I doubt scaling desalinization is as hard as hurling stuff into space, but it may not be easy to scale either. There are plenty of places on earth which are very dry, adjacent to salt water, and extremely rich and yet no great desalinization technologies have come from them.