[giarc]

I think a big reason is you are not notified when someone replies to your comment. It reduces heated back and forth arguments.

[Xeoncross]

Instead, the reply/rebuttal almost always comes from a new person. It makes nice reading when you have 6 people in an argument keeping each other honest vs 2.

[ryangittins]

Interesting, I hadn't considered that! You're probably right.

[Tade0]

Also submissions with more comments than upvotes are looked into, if not outright automatically flagged.