The person doing the PSI likely had the access and time to put together a rather comprehensive picture of Nick and his behavior during the entire legal process from start to finish. They also had access to all the family court records and the information associated with his chemical and behavioral evaluations from that process as well as any testing failures. There would also have been his driving record and the still unpaid tickets. Then there were the letters from Kayla and his father which IMO did him a whole lot of damage through their lack of any remorse argument and their obsession with Nick as a hero fighting for freedom.
Then worst of all for Nick, they probably interviewed him. I'm sure he told the person the "full story" of what happened that he has been promising to tell us. And worst of all, the person doing the PSI might have looked at Nick's social media and streaming activity over the past year. In particular his comments on judges, his attacks on law enforcement & CPS and his general argument that he never did anything wrong.
In court, Nick is just an occasional item on the docket. But if someone starts to document in a PSI a comprehensive portrait of Nick, it would really create an impact.