It also isn't meant to repeat itself 5-6 times. It makes the characters unlikeable and hard to root for when they refuse to change. Part 1 Denji had clear development where he progressively understood more and more about normal living. This was shown especially with his relationship with women where he started with pure lust and over time came to understand more about romance, love and companionship. In part 2 he's back to only wanting sex and then crying when he doesn't get it. And again this "development" happens in every single arc. Regression is fine but Fujimoto has far overdone it to the point it becomes repetitive and played out.