As much as I hate early pulls (like, when it's called out and I get there in less than a minute and they killed it and I'm with a large pack of players all coming) I have to agree with everyone here. It's not against any rules for them to pull it. The only way to curb that behavior is that no one else helps them and lets them die. But people panic when pulls happen and don't want to miss out, so they join to maximize their rewards (thus enabling). But early pullers really only need a few to help them unless it's a particularly hard hunt, which is why everyone just joins anyways. It's unfortunate, but nothing can be done except if you're server sets something up themselves.