I have looked into this, and I know what the problem is with them. Due to them being hotlinked animations they take up a large chunk of bandwidth loading up, and each time there is a thread where a few people have them and have all posted a few times the first thing that
forumer wants to load is the slideshows. I have noticed on other forums that the slideshows have been banned due to this same reason. I hope that explains a little more about the effect of the slideshows on threads.