The profit part of it really came down to "well, just punishing them is leaving money on the table!"

Now, it might be the case that the people profiting from the string and long punishments are so cynical and greedy that they started campaigning for longer, harsher sentences specifically for their own enrichment, but the people are buying it as purification and penance through pain. The prison industrial complex only works as a business because the people already want what's being sold to them.