A dozen is an exaggeration. Your theory OR that his accounts are Staff accounts is obviously mistaken. I'm positive all of Staff here would wish he never existed. The disrespect and harm he generated is the last thing anyone would desire. In fact, for sometime, any mention of his nickname was prohibited in chat, a mod would quickly put a stop as such discussion quickly becomes disruptive (likely by his doing.)
So, back on the topic - Why allow it? It's not being allowed. Unfortunately in todays tech world, it can't be stopped with the open registration process for sites as this.
Besides his sad life, his doings unfortunately have adversely affected too many of our impressionable youth.