I feel like you over-estimate the relevance of co-op/under-estimate online play. The industry as a whole has heavily shifted to an online focus as the average age of gamers has increased to the point that "a feature only a few people will enjoy" is more likely to be local co-op than online co-op especially on PC where a majority of your audience is. I definitely think it's a missed opportunity but it's your vision and I respect that.

if i had designed the game with co-op as a focus from the start then the game would have multiplayer co-op..but it was added on later so i dont want to push the game back many months to get something in that i dont feel like it needs or that isnt the main focus of the game.. plain and simple.