<<Yes, I understand that he's only on trial for the one - and that telling jurors 'he's done this a bunch of times' will jaundice their view, but then why is it OK in other cases like this?>>

Hey Goofy, I think it's because it is a civil case, in a criminal case it probably wouldn't be admissible. (Perhaps Albaby, our board legal expert could offer more insight!)

Criminal law and civil law differ with respect to how cases are initiated (who may bring charges or file suit),
how cases are decided (by a judge or a jury), what kinds of punishment or penalty may be imposed, what standards of proof must be met,
and what legal protections may be available to the defendant.

In civil cases, defendants are not entitled to the same legal protections as are the criminally accused.

britannica.com - What is the difference between criminal law and civil law

All The Best!