Keeping the surface wet is doing the reaction's work
Concrete gains strength through a chemical reaction between cement and water, not by drying out, and that reaction keeps building strength for weeks after the surface looks finished. A wet cure supplies water straight to the surface for as long as the method runs, which keeps the reaction fed instead of leaving it to whatever moisture happens to be left in the mix. The faster surface moisture disappears on its own, especially in sun and wind, the weaker and more likely to dust or crack that top layer ends up.
Letting it dry out between waterings undoes the point
A wet cure only works while the surface is actually wet. Water it once and then let it dry out for hours before the next pass, and the slab spends that gap losing moisture the same way it would with no wet cure at all, then gets rewetted, then dries again. That repeated cycle of wetting and drying stresses the surface more than a steady, unbroken cure would, which is the opposite of what the method is supposed to buy you.
That is also why a wet cure takes more attention than a sprayed curing compound. A compound gets applied once and holds moisture in on its own. A wet cure needs somebody checking it and rewetting it on a schedule, which is exactly the step that gets skipped when a job gets busy.
Stopping it too soon
The first day or two after a pour matter more than people expect, because that is when surface moisture is easiest to lose and hardest to make up for later. Cutting a wet cure short in that window, even by a day, gives the surface a head start on drying out before it has built enough strength to handle it. The slab is not ruined structurally, but the top layer is the part that shows it, in dusting, hairline surface cracking, or a finish that never quite holds up the way it should have.