One of the driving forces behind the story, a big part of the reason why the overall Plot of the story even exist, is that Samui got his Ego smashed by Izuku in what is openly declared a "Simple friendly cooking event with nothing at stakes." That happened just to collect funds for a generic humanitarian organization, even the "trophy" for the winner was just a Toaster.
Samui's reasons for starting what amount to a true Crusade against Izuku have not been explained yet, but one can theorize to be something that cut the man deep in order for him to organize things like blackmailing, Assassination attempts or framing for contraband.
The most likely causes seems to be:
- Bad Mood as an Excuse: "Midoriya got me worked up and I'm gonna take it out on him to feel better about myself!"
- Blaming the Victim: "It's Midoriya's fault for cooking better than me! and provoking me into teaching him his place!"
- Moral Myopia: "I'm the greatest Professional Chef of Japan and I decide who can be a Chef or not, so it's OK to treat Izuku like crap just to hammer my point in for whoever else tries to usurp me."
- Revenge: "Midoriya "attacked" me first! I am just defending myself! He started it by cooking better than me and making me look bad, so me being horrible to him is right!"
- Screw Politeness, I'm a Senior!: "I'm older and have been a Chef for longer than him, so I can be a jerk if I want!"
- The Social Darwinist: "The Quirked survive! Quirkless people are a bane to us! It's our world now, we are the next step of Humanity!"
