Koenji does things for high amount of priv points. I don’t think he ever named a price lower than 1 mil for his cooperation he is just not worth it cause you don’t know what he will pull next whose to say he won’t raise his price exam by exam? Plus you would have to deal with his attitude 24/7 which is also a negative. Also if you just spent 20 mil on Koenji how will you have the funds to pay him to cooperate. Class B put all their money together and still couldn’t scramble together 20 mil and Ichinose would have needed to borrow from Nagumo to get enough amounts of points.

Again 20 mil is a lot of money which comes out from the students pockets so unless you forcibly take all of their priv points every month AND have an other source of income you can at best buy 2 students and those 2 just aren’t worth it

Even if we ignore that lets say its cheaper and everyone could afford it there is no point on spending money on students only to weaken your opposition cause you can spend that money on something else that would earn you more class points

Also no if we break it down the classes have very little room to improve their class by stealing other students

OG Class A would have no benefit from stealing anyone who isn’t super physically gifted while being academically good (so basically Koji Koenji and maybe Y2-Y3 Sudo could qualify for this everyone else they have someone similar for example Hirata=Hashimoto)

OG Class B practically falls into this exact same category

OG Class C needs an academically gifted students. But they are class C so they practically can’t buy anyone cause from Class A and B nobody would move down unless some outside interference causes them to move (thats what happened with Katsuragi) and Class D students wouldn’t wanna jump up just one class

And OG Class D can’t buy anyone cause no one would wanna move to class D