So you don't scam twice as big and just get caught for half of it on purpose. Pretty sure that's Die Hard though.

Because retributive theory of punishment.

How do you rehabilitate a person who does something like this such that they won't do it again? Serious question.

Deterrent.

Well, possibly it could be rehabilitation, but what if rehabilitation fails and they offend again? Do you just layer on more rehabilitation each time, or do you eventually decide on punishment at some point?

Justice

Because there are a thousand other people saying "oooh, what a good scheme. Maybe I should try that."

Deterrence is a significant part of the justice system.

Because otherwise it would be irrational not to commit crimes?