It's also the lazy way to make the campaign harder by adding endless enemies rather than smarter ones. It's been in pretty much COD, but is much more common and obvious in 3arc campaigns, especially W@W (along with grenades) and Black Ops.
The only time you have infinite enemies are the first 2 Alex Mason Missions. It's kinda usefull because you can complete certain challenges without rushing. The amount of enemies is relatively low compared to other CoDs. Like 5 max per wave.
The title immediately gave me an angry face when I thought of that stupid hill in the BO campaign.... I like playing through campaigns with no prior knowledge, and I did really well until that part. I hadn't really played the campaigns before to know/realize that they might just send an endless hoard of enemies for you to have to navigate through to the next checkpoint.
if activision were a physical entity, i'd wrap my hands around its neck and have an orgasm as i feel its pulse slow down" - mega boie715