The reason they are retiring the A-10 is that the airframe cannot be upgraded with the power systems needed to support modern defensive and offensive systems. Modern combat aircraft are giant electrical power systems with an aircraft wrapped around them. When the A-10 was designed half a century ago, this was not a requirement and there is no way to retrofit it.

Modern air defense systems are explicitly engineered to very effectively kill things like the A-10, and it can't support modern counter-measures because of these limitations. It still works in environments for which it was designed i.e. absent modern air defense systems.