That's the number they have, not the number they've published. Only a few hundred are available to the public. Even those are redacted, with names X'd out.
Again, they didn't dump it all. Except as a retaliation for assassination, they're not likely to either, simply because doing an honest review would take decades:
At one cable per hour, it will take WikiLeaks 28.6 years to release them all.
We might find these individual cables to be mundane, but each and every one that has been published is something that a major national newspaper (though not necessarily an American one) thought important.
This is what a responsible publication of a leak looks. It isn't nice, it isn't pretty, and it causes a lot of embarrassment. It also isn't the end of the world.