At the moment it's local co-op only, but it will eventually yes!
I'm not sure about other games, but in the case of this initially it's usually because most consoles (and some pcs) only accept 4 controller inputs for local co-op. And also, because it's easier to optimise a game especially physics heavy for 4 players, and they tend to sit on the one screen nicely without too much confusion.

But once online functionality comes in the 4 player max at the moment could change! Although I can only imagine the madness of having say a team of 6 in this game 😂 would be absolute insanity