The problem is that the presence of infected doesn't need to be limited to action shooty bang bang scenes. There's plenty of ways to include them in tense stealth scenes where the characters have to sneak past them. It doesn't have to have a long run time, just 2-3 minutes of them having to sneak past one, a cold open in episode 6 or 9 where they open in a 30 second chase sequence running down the hall and they have to barricade a door with a dumpster like in the game to get away from some infected... plenty of ways to insert the ever-present threat without having to use a ton of resources. Yeah maybe the visual FX would have cost more...but come on. In fact having shootouts with the infected would do less than having a stealth section.