Why is Andy Kaufman so funny and AKS so not?

It has to do with context. Andy Kaufman's personas played with the formality of public performance at a time when things like talk shows, comedy acts and sports events pretty much offered a predictable, familiar experience.

There is nothing formal or predictable about youtube. Culture has moved way past that and so trying to make a farce of something that itself has no form or standards doesn't have any comic value.

You can't subvert expectations that your audience doesn't have.

This is why what Andrew WK did is funny, and why this isn't. The juggalos were expecting to have the experience that was marketed and sold to them.