The same thing happens in state sentencing. There's a vast gap between minimum and maximum sentencing. Most sentences fall somewhere in the middle, depending on the details of the particular act in question. (You stole from a little old lady versus stealing from a drug dealer, for example.)
Doesn't that lead to vastly unfair sentencing? For example you could target a specific group with harsher sentences, or use minor crimes to stick people with the maximum sentence. Everyone is guilty of something.