After re-reading: you avoid prosecution by not being a large enough offender, or by offending in a jurisdiction where law enforcement is not trained to catch you. Not all that different than avoiding prosecution as a recreational drug user when the cops are too busy going after bigger fish.

There's a lot of time and resources spent in between the time of identifying that an IP address is broadcasting CP to having all the information you need to bust down the right door and lock up the guy for a long time.