If the original Trump fine had been 10 million the judge would probably have reduced it to five million. I don’t remember what it’s called, but in bargaining you create an expectation with the first offer. If the other side gets down to half of it, he views it as a win. Whatever the item is actually worth isn’t relevant.
Also, the judge wants to reduce the fine, but not piss off half the electorate who wants it even higher. (Let’s face it, they want Trump dead.) Given all the various perspectives in play, this is probably as good as Trump was ever going to get.
Trump did have additional leverage, appealing to SCOTUS.