Because, after ten years, he will get out and become a model citizen. Right? If you don't deal with the root of the problem, the monster you create will be your undoing. If the feds keep doing this, it won't be pretty. They are creating a lot of monsters.
What do they care? Their children and families are secure in their gated communities. Creating more monsters just means expanded power and job security.
The monsters and power-hungry need each other to survive and flourish, and they prey on the rest of us to do so.