Bluegrass does have favorable soil temperatures for germination during the summer in many regions. I sowed some seed on the 19th of this month on a couple troublesome tall fescue patches I killed off earlier this year, just to see how summertime sowings work. If reasonable germination does not occur for some reason, there should be enough time left this season for another go. We've had favorable rains this summer though, soil moisture is good at depth and the turf didn't ever enter dormancy.
The key for Blugrass germination is to keep the soil slightly damp for AT LEAST two weeks straight. Not soaked or waterlogged, damp. This may mean several light waterings daily in the heat of the summer. I think that's the problem. It's one thing to fill in patch or two, but large areas would need careful monitoring. Cooler fall temperatures and the probability of a little help from mother nature increase the odds of success.