Essentially, chat slowly became a more hostile environment, where different people would fight all the time, and it escalated over time. Other people took sides, fights spilled over onto the MB, Mike and whoever else was in charge had to deal with constant complaints and requests from each side to do something about the other side. This lasted for some time without end, until some of the people on one side were banned from wotmania. The bitter feelings remain.

That's the more or less objective version. My less objective version is that some people were complete assholes, some other people did not like that and laid some admin-power smackdowns, the assholes got worse, the smackdowns got worse, people took sides, it became a debate of assholery versus abuse of power, and eventually it was decided (too late in my opinion) that the assholes had gone too far in their disgusting assholery, and they were banned. Throughout this process, everyone not directly involved became sick to death of hearing about it, especially the people running the site. Chat turned into a barren wasteland for a time as no one wanted to go there anymore.

EDIT - I'm not pointing fingers or saying anyone was wrong. I have my own opinions and I'll leave it at that. I just wanted to answer the question, I don't want to dredge up any bad feelings. Which is precisely why I'm not entirely in favor of having a chat on this site, y'know?