Blizzard games aren't known for being intensive on PC system resources, but I would have never thought that almost a quarter of players of the PC version of Overwatch are using integrated GPUs. According to Blizzard 22% of Overwatch's PC player base forgo a dedicated graphics solution in favor of Intel's HD Graphics or AMD's APUs.
Blizzard Senior Software Engineer Ryan Greene spoke on the Overwatch development team's hardware compatibility goals at GDC 2017. He stated that the goal of the team was that the recommended specs should get at least 60 fps, and the minimum specs should get at least 30 fps. Greene said not everyone on the team was excited about optimizing the game for low-end hardware, but as time went on, they started to see the value in the concept.
During play testing for Overwatch, Blizzard used various configurations of hardware, from top-of-the-line gaming PCs to notebooks and ultrabooks. Green stated, "We set up playtest labs with various machines all configured with different hardware. We got different people to play on it, and they were surprised at how well it ran, and how much it felt like Overwatch."
Perhaps one of the aspects that has made Overwatch so popular is its accessibility. In the days where many AAA games get a token unoptimized port to PC, that even high-end hardware have trouble running, a game that can run on almost anything might make a PC gamer out of someone with lower-end hardware who would never consider playing on their machine before.