CoD uses its own developed and maintained engine, so no royalty share with Epic. (Big deal with those sort of sales numbers)
Cold War was also very content rich by the end with a campaign, full multiplayer suite, 2 versions of Zombies (round/mission map based plus an open-world variant using Warzone assets), and a bunch of unique minigames and even emulations of old Activision games.
Oh, and obviously it was loaded with MTX as a full-on GAAS and even began the integration with other franchise entries.
It was extremely self-evidently a fucking huge project.
Oh and at least it ran on Xbox!