I find often times people (sometimes women more) often don't understand the level of addiction inappropriate contentography has. They will think of drugs and what not. But drugs are not the same really. Drugs are not around you everywhere you do. inappropriate content or just sexual looking things are everywhere thanks to technology. Games, movies, tv, books, ads....etc. Phones, PCs, tablets, big screens...etc. Even the way people dress can make you think naughty sometimes.
So trying to stop the addiction is VERY hard. For every person that claims they stopped overnight, there are 99 other men who are still struggling or it took them months or even years to stop. And even then it doesn't mean you are free for life. You can go 40 years without looking at inappropriate content and suddenly theres a crack exposed in you and the devil runs in to make you screw up.
Beyond that the scientific reasons for why its hard to stop has to do with many aspect of how our brains works and chemicals and what not.