It's not as if "he was mistreated by an insurer" is a defence, is it? That should be entirely irrelevant to the jury's finding, although sentencing might take it into account. The jury just needs to decide if he did it, so not having been mistreated by an insurer shouldn't preclude someone from making that decision.
'Shouldn't' is true. But the prosecution does not need to explain why they reject a potential juror by 'preemptive challenge'. Why would they take the chance?
Similarly, a defendant's race is not relevant to their guilt, but you're not going to pick a self-declared racist if you don't have to.
