(nearly 3.4 million violent victimizations per year) went unreported to the police between 2006 and 2010."
As others have reported, as the population loses trust in the ability of the police to prevent or investigate crimes, accelerated by police defunding, reductions in services like 911, revolving door "bail reform" and other developments, fewer victims and witnesses will report crimes.
Link: https://openoregon.pressbooks.pub/criminologyintro/chapter/2-3-the-dark-figure-of-crime/