https://www.gamespot.com/articles/e3-2018-why-its-called-gears-5-and-not-gears-of-wa/1100-6459850/

Microsoft announced a fifth Gears of War game on its E3 2018 stage, but it's not called Gears of War 5. Microsoft announced the title as Gears 5, and that was no mistake. Speaking to GameSpot, Xbox marketing boss Aaron Greenberg said the Gears 5 title is "cleaner," not to mention that people were already cutting out the "of War" part of the title for years already, so it was a natural change.

"People shorthanded it Gears anyway," Greenberg said. "It's a cleaner look for the brand and the line. Of course, the franchise is still Gears of War."