Cops dislike paperwork, but many of them also don't give a shit about their jobs except insofar as each day gets them one step closer to early retirement, with the payout based on whatever overtime they were able to rack up a few years prior.

Sure, people should just decline to share any information with police and many police won't push the point because it won't play out well. But some portion of the desirable assignments will flow toward those eager beavers who most assiduously supply the desires of the brass for more information. Legalities are one thing, the incentives and internal dynamics of the police department are something else, and they don't always line up neatly. Furthermore, not all police officers are rational utility maximizers who base their decision-making on optimizing their future wellbeing.

The gist of the article is not 'you're being passively victimized again, oh no' but nor is it, as you point out, 'they have nos uch right so don't be fooled.' The news here is that LAPD management have instituted a policy of maximizing data collection for pre-emptive surveillance purposes, which is something quite different from individual cops being overzealous or prosecutorial standards having shifted.

I think it's reasonable for the writer to be descriptive rather than prescriptive, and that it is not his job to act in loco parentis or in loco advocatus.