Cause this stuff is illegal and high profile. And Uber has been skating if not nakedly flaunting the law for a long time now. If the DA starts sniffing, people are going to start talking.

Furthermore, the odds of the leaks continuing approach certainty at this point. Even in a civil trial, who would perjure themselves over a job? (Pleading the fifth is a potential option even in a civil case, but is real problematic and probably will make a criminal investigation even more likely.)

The judge has referred it to the US attorney (prosecutor) for possible criminal prosecution. The big new piece of evidence today (the letter) was given to the judge by the US attorney as relevant evidence they have found. So there is clearly an ongoing criminal investigation into the same thing.

Evidence of criminal activities could become apparent during a civil trial, and lead to subsequent criminal charges.

Plus perjury, etc.

"The letter said an organization within Uber called marketplace analytics “exists expressly for the purpose for acquiring trade secrets, code base and competitive intelligence.”

That sure sounds like illegal activity, in fact lots and lots of it.