Maybe because the poster characterized the problem as: "So then, is the complaint simply that Cook is not providing direct evidence of these claims? Is that a reasonable expectation? What evidence could Cook provide that would directly tie violence (we know that Hong Kong protesters have committed violence) to this particular app?"

Whereas the article says: "The first allegation is that “the app was being used maliciously to target individual officers for violence”. This makes no sense at all. The app does not show the locations of individual officers at all. It shows general concentrations of police units, with a significant lag. As the developer and @charlesmok, a Hong Kong legislator, have pointed out, the app aggregates reports from Telegram, Facebook and other sources. It beggars belief that a campaign to target individual officers would use a world-readable crowdsourcing format like this."

It could be incompetence, but it seems much more like clear disingenuousness, which is a pretty common thing nowadays.