It’s possible to even go to the station, speak with the on duty officer, find out that they’ll basically do nothing and decide to not waste any more time on that. Such a conversation will not show up in any statistics, ditto an equivalent phone call.
For substantial losses, insurance claims make more sense. If it’s something that’s close in cost to the deductible and you expect your insurance premiums to go up after a claim, most people would not even submit that - there is not much pay off and higher premiums to worry about. So a lot of these costs are basically absorbed by the victims and statistics end up looking better than they should.
In my general area, 20-30 years ago, I’d sometimes forget to close the front door when I left (as in wide open, visible from the street). Nothing ever happened. A year ago, I forgot to lock the car at night - interior got ransacked and turned upside down. There wasn’t anything of value in there, but it sure left me feeling a lot less safe…
Because your insurance demands a formal report (because if you lie to the police it's a marginally more serious crime than if you lie to your insurance agent).
What I can see causing a drop in reported crime is a lack of trust between police and a community - people may choose not to get the police involved out of fear they will make the situation worse, overreact, or may deem the punishment too harsh.