Heat is probably the main cause.
Found this on the internet - Nuisance and filth flies like the common housefly will multiply more quickly in hot weather. Under normal conditions, housefly eggs take around 20 hours to hatch into larvae (maggots). But when the temperature hits 99 degrees Fahrenheit, those eggs can hatch in less than 8 hours.
20 hours versus 8 hours - quick turnaround for those baby flies.
Drought could be a cause too. Farmers are getting rid of livestock as they can't afford feed. Less poop to attract them there.
Increase in pets - poop attracts lots of flies due to smell. so if not being cleaned up well this happens.
Everyone staying home and enjoying vacations at home also could be a factor as there is such much food and drinks in the back yards which would attract flies.
August though is a high number of flies season almost every year. Just started earlier this year. At least for Douglas.
This website has some ideas which can help.
https://www.healthline.com/health/how-to-get-rid-of-house-flies#:~:text=A%20mixture%20of%20vinegar%20andthe%20glass%20with%20plastic%20wrap.&text=Flies%20will%20be%20attracted%20towill%20fly%20through%20the%20holes.