Its about taking care of as many problems all at once, and as cheaply as possible.
Any way you work desalination it has to be pumped to the highest point and gravity fed as needed. And if possible without building new infrastructure!
Salton Sea has got to be taken care of and soon or there will be such toxic dust blowing throughout that the area will be inhabitable.
Since trying to put fresh water into the Salton Sea to desalinate it to acceptable levels isn't currently workable, the canal allowing ocean water would do that and bring the area back from the brink of destruction. And since (hopefully) desalination as a necessary water source won't be permanent, its capacity when not needed could also then be used to keep the Salton Sea at acceptable levels... another words solving both problems at the same time.
Currently they have two solutions to solve the problem with the Salton Sea, both are half ass and not well thought out. The current plan thought to be the cheapest only fixes part of the problem and hasn't been funded at all in the last 40 years. Estimated I believe at 9 to 10 billion and does nothing. The Eco system their is dying and hasn't much time left.
There's also a possible third benefit of such a system. More water from down south, might also permit enough water to be retained up in the Owens Valley area to help solve the problem there which is already in the works, but I don't believe funded either.
Legislator can solve the problem or keep talking about it.
