Ok, let me give you an example. Big companies hold their certain share of the network. If they try to destroy each other, it's possible that only one will dominate at the end. Rather than taking a chance to be destroyed, they come to an agreement and maintain their profits (continue mining on their equipment and continue slowly selling equipment). Reasonable?
But I guess with hashing ASIC design being pretty simple, too many new companies are popping up. So yeah, it probably wouldn't have worked well.