Even if they investigated each and every name (which would take WEEKS just for one fixed list) the botters would just get a new one, usually a phished account or purchased with a stolen credit card.
Since stolen merchandise is involved and chargebacks cost them money it's better for them to NOT take out the bot accounts right away and instead either cast their net wider or try for IP bans (which rarely work thanks to VPNs)
It's kinda like dealing with bees. Killing individual workers isn't going to make the problem go away.
Of course, if people would stop being stupid and going to these sites in the first place we wouldn't have a botter issue at all. Some public awareness of the issue is in order.