It only makes sense if the Sith truly believe that they are the good ones and that that struggle for power strengthens them and at the same time ensures that the best Sith is always running things.

On the other hand, having about 1000 Sith is probably better for their purposes than 1 really awesome guy and an apprentice.

I've been thinking of reading the Darth Bane books. I can't find them in audio ANYWHERE and I'm not sure I want to read them well enough to, you know, actually read them.