Long prison sentences and insignificant fines: Why?

I was reading the Wikipedia article about Ronald Pelton, a former NSA intelligence analyst turned Soviet spy:

(bolding mine)

This is something I noticed before when reading about (usually Federal) criminal cases in the US: A defendant is sentenced to serve an extremely harsh prison term in conjunction with a ridiculously low and insignificant fine. Why do they even bother? The court decides to lock up an individual for life (Ronald Pelton actually spent almost 3 decades behind bars), a punishment which is as overwhelming and life-changing as anyone could imagine, but/and at the same time, they order him to fork over some small change? What’s the reasoning behind this?