but shouldn't be punished?

Here are some of the reasons the judge gave for the heavy fine:

1. Part of the reason was because of Trump's history of fraud.  There were the settlements for fraud by Trump University and the Trump Foundation.  The felony tax fraud conviction in 2022.  "This is not the defendants' first rodeo."

In other words, it's obvious he's going to keep breaking the law unless he gets more than a slap on the wrist.  Same thing happened in the E Jean Carroll case.

2. Additionally, the defendants refused to acknowledge they had done anything wrong.  "Defendants’ refusal to admit error—indeed, to continue it, according to the Independent Monitor—constrains this Court to conclude that they will engage in it going forward unless judicially restrained."

3. See also the link below for the reasoning for this conclusion by the judge: "That the Trump Organization has taken to manufacturing its own version of its assets [under the supervision of the court-appointed monitor], one that fails to include any valuations, is a telling admission that it simply cannot, or will not, prepare an SFC without committing fraud."

If Trump didn't want to get hit with such heavy penalties, maybe he shouldn't have committed fraud over and over and over again?  Or at least shown contrition and said he wouldn't do it again?  Or taken actions under the court-appointed monitor to put proper financial controls in place to establish expectations that he won't continue to commit fraud?