We know Kurt designed the guitar. But, many of us also know that you aren't going to get that sound you're after with the Jag-stang. At least not unless you are willing to mod the JS, buy up every piece of equipment he used, find all his settings, and even then...you will only get his live sound.
This is something most of us already know. We are also ok with that.
As for why they own a Jag-stang, I really can't speak for the other members, but I bought one because of Kurt. I'm sure many of here did. So what? Play your guitar, write some stuff, be happy. What else can I tell you?