Because there's only one article on each topic.
There's a zero-sum thing to fight over.
If you want a given perspective represented on the target article, you'll have to engage in debate with the other people with opposing views and make a stronger case to win out.
Debate is hard, so all else equal, people tend towards territory that is unowned, to avoid having to fight.
This leads to diffusion by default: default-divergence.
But if there's a scarce resource that you have to fight over, then it pulls you into it and forces you to debate.
The debate leads to a high-quality outcome.