Need help with integrating marxist theory into sci fi

Hey! I'm currently in the process of writing a sci fi novel and as a philosophy student, am obviously bringing marxist viewpoints into it.
I have a specific question in which I would need some help, since I am not really sure how to "work" with a specific element of my world.

So, in this world, production of machines has been so heavily developed, that they can essentially do any jobs a normal human does, while being cheaper to produce then it is to sustain and manipulate the working class. The ones profiting from this are mega corps and to some degree the logistics personel, which is "thinking" for the machines, as they may be cheap and able to work, but lack the minds to do so (artificial intelligence is not really a thing in this world.)

So, my question is, why doesnt the bourgeoisie just get rid of the surplus, those people who aren't needed for them, when producing machines is so much cheaper?

I'm aware of the reserve army of labour and that is certainly a good reason. There is also somebody profiting from their existence, a security firm.

Maybe its the scale I'm working with? I'm not talking about a few hundred thousand people, but millions barely having what they need to survive but continously getting shut down by this overpowering security firm.

I hope questions like these are allowed, if not I formally apolagise.