Do you have a dog? And is it a she?

Or too much water. Grass needs about an inch of water per week and that includes rain water. Also watering as few times as possible helps roots grow deep so the plant is resistant to drought. I usually water once a week, if the soil is sandy then 2-3x a week might be better. Worst of all, constantly wet soil promotes fungus. I'd suspect fungus issues first.

Have you ever had your soil tested? Do you fertilize? When and with what?

Agree about the watering. Daily is never a good idea, even in very dry climates (which yours is not). Watering deeply but infrequently is the key. Once a week should be plenty.

It looks like there may be some annual weed grasses mixed in with the lawn grasses and it is possible that these have now died off or gone dormant leading to the patchy appearance.

To confirm the presence of a disease, take samples of the dead portions (or what appears to be dead) into your local extension service office. You can find your county office HERE.