The only advantage of a such name is uniqueness (more precisely, a google-wide uniqueness), but why exactly is that an advantage?
Perhaps to make it easier to track which sites were successfully attacked? For example 100 000 websites under attack, 100 000 silly user names; a month later an automated google search reveals which websites are insecure, and those are selected for a second wave of attack? For example, to avoid Google penalty for getting 100 000 links on the same day, the spammer could create accounts on 100 000 websites the same day, but only add 200 links a day from the attacked sites to their own websites.
This was my first idea, but... why google for a unique username associated with a website, when you can just look at the given website to check whether the user's wiki page still exists? (Is the Google search perhaps more anonymous?)
There is an added bonus that it is harder to link related attacks and find out which group is behind which wave.
Also, there will always be some amount of legitimate users with random names - and any other easy to generate will-always-exist pattern would fall into collisions more often.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.