Because once someone has served their time and their probation the idea is that the state is saying their debt has been paid and the state no longer believes them dangerous. If that's not the case then there's a problem elsewhere and you're just treating symptoms (futilely I might add).
An even bigger problem is presented by the "etc." If it was the convicted child molester and rapist list that would be one thing but the etc contains a lot of other offenses that don't justify restrictions designed to stop child molesters from repeat offending. Maybe there should be a proposition to split the lists by the a Specific offenses so at least these measures could be targeted better. This prop also played fast and loose with the definition of sex offender IMO.
I don't think this is strictly true, otherwise an "incurable" paedophile would never be released, regardless of whether they have completed their sentence.
I take your point about the "etc". It needs to be serious, predatory offenders, not 15 year-olds sexting each other.