It became a real problem on reddit after a while where bots would just go grab the most popular posts of 6 months ago and post them all again. Before the bots, people would do it to farm karma, and the people would get called out for it, but it was never a huge deal because you were still getting at worst like a 60/40 split of new content to reposts. But after a certain point the ratio shifted dramatically in favor of reposts in a lot of bigger communities. I think that's what really galvanized the hatred toward them.