Very true. AT&T is not required to make sure that cities have good coverage.
I think all carriers, not just AT&T, want all the coverage they can get so as to not lose customers.
I don't believe AT&T decided to un-cover your area deliberately. It is not in their best interest to anger customers or eliminate entire districts from their network. In some cases there are towers that belong to local companies who refuse to lease access to Carrier A because they already have a commitment to Carrier B. In some cases there simply is no coverage at all for any carrier.
You may want to ask others in your area what providers they use and perhaps find better luck there. Years ago, I chose AT&T because they were the only option in the town I lived in. When visiting friends in certain areas of Long Island, I'd lose all coverage completely, and everyone who lived in that town used Verizon. Today, both carriers have coverage there. I was in Hong Kong two months ago and couldn't make a call from an iPhone I'd used there a dozen times. They changed partners and they used a different band. It's a fluid situation.