That is the point, because you water so frequently the roots don't go deep enough, it's a cycle. Set your mower to the highest setting and soak your lawn to soggy once/ week or twice a week depending on the temperature. Your lawn will LOOK better in the long run. It's best to start this in the spring before it gets too hot so it might be too late to try this now. By watering more you are creating a situation where you HAVE to water more, if that makes sense.
Almost all "grasses" are weeds. Weeds don't need anything to grow. St Augustine grass is a weed from Africa, if it can grow there and exceptionally well in Florida without regular lawn watering. And almost every area I've lived in, has strict watering rules, especially Florida.
I went to Scotts testing grounds outside of Orlando, beautifully manicured lawns there, and they don't have to water the lawn at all. They've seen St Augustine grass grow nearly 5 ft tall with roots 6 ft deep in the ground. It was in the backyard of an abandoned house. Guess what, it didn't get anything more than seasonal rain. That would be one perfect lawn once it's mowed.
Always mow your grass on the highest setting in the summer, the longer the grass the more water the grass can hold. In the spring and fall you can cut it to 2-3" short.
When you soak your lawn the water is allowed to go deep into the soil (more so than you think), and the roots will follow suit. The deeper the roots, the more water it finds and the less you need to put on top. You also run into a number of other problems with short roots, causing it to die even faster.
HOA's are the biggest to blame in people thinking they need a perfectly manicured, watered every day lawn. Lawns are the biggest water wasters in this country. And almost all types of grasses can be grown without anything more than seasonal rains.
But the corn was fine and so was the water bill. It doesn't seem to run it up as much as you would think it might. 
