99.9% of people want to play co-op

That has not been my experience.

Quite a few people insist they're playing solo and act as though all the other players are NPCs

You also have a real problem of distance rendering, such that people outside your visual horizon seem to stop existing for much of the population.

The weird thing is if players simply worked together to fight back we could have co-op mode.

fairly certain it's less than 90% that want to play co op