It's been proven time and time again with Call of Duty that once it has a good thing going, and fans are happy with the current formula, then it should just stick to it. Follow-ups like Zelda: Breath of the Wild and Mario Odyssey were received so well because of their decision to switch up the franchise formula and produce a new but comfortably familiar experience.
It's usually the case that fans of a series will want a sequel to switch up the formula for the next entry in one way or another, whether that's through the gameplay or through story context.
In most video game franchises, innovation is a key part of success. As the most recent release, Call of Duty: Vanguard didn't fare much better with critics or fans, with generally better received gameplay that was still not quite as hard-hitting or tight as Modern Warfare's offering a few years ago. The gunplay in Cold War also felt oddly weightless when compared to Modern Warfare, making it feel a little outdated. Call of Duty Black Ops: Cold War attempted to add its own mechanics to the franchise, but this only bogged down the experience. Since its release in 2019, two more Call of Duty titles have released, but neither one has managed to capture the same feel Modern Warfare. The pacing of the campaign was also pretty good, with a decent blend of slow-paced missions complimented perfectly with a fair amount of bombastic action sequences.
With state-of-the-art cutscenes and stellar voice work, Modern Warfare's story is one of the more compelling narratives in the franchise, and with a handful of returning fan-favorite characters, Modern Warfare acts as the perfect reboot. On the campaign front, Call of Duty: Modern Warfare had a fairly solid one.