Most desal plants are producing in the tens of millions of gallons per day range. In order to get a proper evaporation, you're going to need a whole lot of surface area. Just not practical.

Plus, not as simple as concentrating evaporating seawater to get salt. You gotta separate your other type of salts that will form once the brine saturates.

The problem is though, its cheaper for salt consumers to buy mined salt than from desalination plants. To concentrate seawater enough to create a viable salt product from the brine would take 4-5x more energy than simply desalinating for potable water use. That is on top of the 2-3x more capital equipment you'll need for this process. It doesn't make it economically feasible to do so (at this time). There's promising technology that's being researched and piloted, but until there is that gap is filled, then desal plants are going to keep dumping concentrate back from where they got their water.

Keep in mind that this $2-$5 per m3 capacity is capital equipment cost (with civil/install/etc ) only. OPEX is an additional 3-5 kwh/m3 produced, which costs can vary whereever you are on the planet.

Seawater desal, specifically reverse osmosis, has a lot of detractors who don't like it because you you're generally getting a recovery of about 40-50%. Which means you're dumping more than half your high salt concentration brine back into the water. This is water that has 2-3x the salinity of the ocean/sea, so there is rightfully a lot of concern about destroying the environment/ecosystem.

There's a push to improve the recoveries in desalination, but the cost is always it requires even greater energy consumption.

Personally, a mix of seawater desal and wastewater reuse would be the best solution for growing water crisis.