That assumption is predicated on law enforcement being willing to publish statistics on their actions. You can't have this work without that. Considering how often SWAT teams are unnecessarily used and the military tactics they employ, the results will be unflattering to police departments.
Of course they don't want their time wasted, but they won't trade transparency and accountability for it.
Because signing up is still a chore since you need to choose the right instance and hope they don't defederate from an instance you like content from. Instance? Defederate? Then you worry about whether an instance can handle more traffic from other instances before it gets too expensive to run. And what about when so many more instances come online? It seems like the amount of syncing is multiplicative, so we're not sure how bad it will get when you have a bunch more instances, because it's a problem Lemmy and Kbin haven't had yet.
There's a lot that's not ready, from signups bugs to quality of life problems (how many people are subscribed to a community/magazine? How do you find out? You go to each instance because each instance only tells you how many people from that instance are subscribed, not total). I want to believe this is going to take off, but it needs to get better before the average Joe will be able to easily use this.