Scanlators need to be willing to indirectly call out members who don't do their job and request someone apply to replace them. I've seen them fail to do that again and again, or only do it after everyone has already lost interest in their version... If they don't do that, what happens is that a one-man scanlator shows up and usually does a worse job on everything except the one thing that was missing, when they should have just joined the original group.
Of course, the one-man scanlator is still the hero in this situation, for stepping up when otherwise there would be no chapters.