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You're still fundamentally conflating "aren't logged" with "are logged, but chats expire".

Consider what would happen if a company deployed a system of microphones across their offices such that all in-person conversations were logged. They'd then look at these logs, discipline people based on "private" exchanges etc.

Then when they got into some legal trouble they'd say "oh, we'll keep the microphones and surveillance practices, but expire the records after X days".

That's fundamentally different from the situation of simply removing the surveillance. A court could very reasonably conclude that the company is structuring its affairs in such a way as to avoid court oversight.

I've worked at other companies with similar expiry policies. It's well known in the industry that everyone does this to avoid discovery.

For the employees it's the worst of both worlds: You don't get privacy, and you also can't look up some valuable exchange that happened 90+ days ago.

I think the courts are right to call companies on this particular line of bullshit, and very much doubt that the government could force companies without the proverbial microphones everywhere to install them.