How often do you think an individual piece of debris is impacting other objects? Most space debris starts as something in orbit, and if it's at a high enough altitude, most pieces do indeed stay in orbit. There is clear precedence for this.

https://swfound.org/media/6575/swf_iridium_cosmos_collision_...

"Analysis by both NASA and outside experts indicates that more than half of the Iridium debris will remain in orbit for at least 100 years, and much of the Cosmos debris will remain in orbit at least 20 to thirty years."