Yeah, just like Call of Duty isn't about multiplayer. Single-Player is a great PR flag but you'd have to be delusional if you think ArmA is a Single-player experience first and foremost. It's a huge milsim sandbox that has a strong core group that cares about the MP aspect, not about some shitty voice acting. Developers and publishers always want to push SP aspects despite being a smaller focus piece, it sells games and is easier to show off but it isn't what makes people stick around, thus it's less important in the long run.
It's not exactly easy showing off an MP scenario at every press event or in every video, as MP games have a habit of being extremely inconsistent and not really show off the developer vision.