It is!
- Introduce a campaign only game, and people complain about the lack of multiplayer.
- Introduce a multiplayer only game, and people complain about the lack of campaign.
I really dislike the mindset that tries to dictate the vision of a developer's game, rather than enjoy it for what it is, if you find it appealing. I'm glad Splatoon has a campaign mode, but from day-1 Nintendo demonstrated the core hook of the game is the multiplayer, and I had absolutely no problem supporting that vision.
Granted, having both modes doesn't hurt(though there's usually an internal development risk of divided attention), and there are some obvious cases where adding either mode seems like a no-brainer. However, it's unfortunate that some people treat having both modes as though it's an absolute requirement, even when it's unnecessary to the vision, core elements, and ultimate enjoyment of a game.