A. The city has incentive to hide the actual numbers[1], and B. Most business owners don't bother anymore with reporting, because what's the point?
I'd say it's probably a combination of the above.
Edit: [1]Because it is an election year. High crime looks bad.
... and cops have an incentive to overstate them.
For example: https://www.businessinsider.com/nypds-shake-shack-hoax-stop-...
I don't find that argument convincing.
There's a grim and extensive investigation at https://knock-la.com/tradition-of-violence-lasd-gang-history... of this.
As an example, the NYPD doxxed DiBlasio's daughter in revenge for his position on the George Floyd murder: https://www.newsweek.com/nypd-sergeants-benevolent-associati...
Overstating/cherrypicking crimes is a frequently utilized PR tactic to fight attempts at police reform, budget cuts, etc.
For example: https://twitter.com/dceiver/status/1493643563892150278
"Shooting incidents are up 500% in an East Harlem precinct compared with last year" winds up describing going from one to six.