In the discussion of space junk, and kessler syndrome, there is a large bias that needs to be addressed. Most commentators operate under the impression that most of the stuff up there is "junk" from human activities, that space was essentially clean until we got there. It wasn't. It isn't. There are literally tons of natural rock falling onto earth every day. By some measurements over 100 metric tons per day. That is only the stuff actually landing on earth. Exponentially more of it passes by without striking the planet but nevertheless still passes through the orbits of our satellites and space stations. Worse yet, because we have a large moon, much of that will have itself entered into some form of orbit around earth. Any discussion of the dangers associated with human-created space junk must occur in that context.

Why hasn't the kessler syndrome started already? Why has the ISS not been sandblasted after 20+ years in orbit? Those are great questions.