Many people have multiple names, and the majority of them abuse the names they have by cheating abuse etc etc.
However, some people have multiple names because they want to have one name to play purely for points, and another name they can use to mess about with and chat with their freinds, without having to worry about their points.
The reason they register the various names is because it is increasingly hard to get a game if you do not have points that an opponent can take from you.
Couple that with the fact that non subscribed players cannot challenge very many people, and you can see why some people are willing to pay the extra and have another name.
Basically, if you want to be able to play a game at your own leisure, you need to be subscribed in order to be able to challenge people effectively.
I dont know if this a good idea, or a bad one, or if this was the original intention when the challenging rules were changed. Regardless of the intentions though, this is now what appears to have happens, and is partially responsible for multiple names.