By using sprinklers on the surface, where it is hot and dry and highly evaporative, roots come to the surface and become highly dependent on continued irrigation there.  It's a never ending cycle of waste when you irrigate with sprinklers.

By irrigating underground, roots grow deeper and become better able to find water already in the soil from natural sources and from residual irrigation.

And with their roots deeper underground, trees won't come ripping out of the ground in a windy rainstorm!