I'd wager that those lawns have been overseeded with one of the winter ryegrasses, a cold season grass. Ryegrass dies out in the summer season, leaving a struggling warm season grass species to try to recover.

If so, it's one of the worst things you can do to your permanent grass. Trust me. The practice is adopted from the golf course industry, which is driven by necessity to have green greens all winter in the south. But golf courses are the most expensive real estate in the country. It takes a heck of a lot of chemicals and maintenance to maintain ryegrass over the winter. But the primary problem is that your permanent grass is weakened, making it more disease and weed prone.

Lawn care companies LOVE to sell overseeding as part of their program.
Bright green grass looks fake in the winter, in the south. A spotty, weedy summer lawn will be the result.

I seeeeeeee.

By the way, ryegrass is sold in the fall and winter only. It truly has different physiology than warm season grasses.....it will die out in the late spring/early summer leaving a stressed out permanent lawn for you to deal with.

My neighbor has his lawn overseeded and now has to hire Chemlawn to make several visits a year. :-(