I'm not sure. What you don't understand is that the law is meant to lay out the rules and the sentence is there to punish the criminal and set a PRECEDENT to potential future criminals.
What the gov't is doing is using a VERY high profile man, who did a very bad thing to a very loved species, as an example to all the other ghetto mother fuckers who think it is cool to fight innocent, defenseless dogs for entertainment purposes.
They are using this as a deterrent to others. Vick is being made an example of.
This is the way of life.
Telling a brother down the block that Vick only got a $200 fine for getting caught dogfighting would turn into them essentially saying "Fuck it, it's only a $200 crime."
Making the penalty SO stiff is what helps prevent the crimes from happening again.