Call of Duty series didn't shy away from real-life locations or countries before but it appears that issues that arose from featuring them made Modern Warfare settle for a fictional nation, called Urzikstan.
Call of Duty: Modern Warfare is the latest in a line of video games that gave up references to certain real-world locations due to the mounting pressure from several entities, including countries, regarding the apparent misrepresentation. One of the most prominent cases before Modern Warfare was the one with Ghost Recon Wildlands when Ubisoft found themselves in trouble with Bolivian government over the fictionalised depiction of the country.
Years later, Ghost Recon Breakpoint is set on a fictional island called Auroa. It seems like Activision wanted to bypass legal issues with countries altogether with the upcoming Call of Duty: Modern Warfare. The game's campaign will have a chunk of the story set in a fictional Middle Eastern country called Urzikstan, where certain terrorist attacks originated and where an allied offensive is taking place.
Polygon interviewed Jacob Minkoff, singleplayer design director at Infinity Ward, during E3 2019 and inquired about the reasons for going with a fictional Middle Eastern country even though US and Brittish troops come from actual countries that exist in real life.
According to Minkoff, the reason why the developers felt it was fine for western troops to have real countries behind them is that western players could relate to their motives. Meanwhile, they apparently felt like they couldn't depict the intricacies of Middle Eastern countries faithfully enough, without getting themselves wrapped up in the politics of any given country.
Furthermore, having to worry about accurately depicting real-life parties would put constraints on the creative team and their vision could potentially be compromised.