The prosecutors piled charge upon charge. If they didn't want 30 years, why pile on so much? If they wanted 6 months, they could have stuck with a charge whose sentencing wasn't so extreme.
They pile on charges so that they have options. They will throw every possible thing they can think of at you and all they need is a couple things to stick and they have their win. They can drop some during negotiations to appear to be working with you. If they come at you with one single charge, you have a greater chance of finding some technicality that gets you out of it. Defending yourself against one accusation is far easier than defending against 10.
Double jeopardy (the U.S. Constitutional guarantee against being charged with the same crime twice) basically requires that the prosecutors bring every viable charge that they feel they have the evidence to support for a given single crime.
The flip side to this is that sentences are normally given concurrently, or simply based on the most serious charge actually found guilty of during the trial.
