Because he believes traditional blue-collar jobs (construction, truck driving, welding, etc.) are going to be automated, and so are obsolete. He has deluded himself into thinking that robots will magically perform traditionally physical jobs, while believing his job, and jobs like it, can never be replaced by machines, which makes him the real working class (those YouTube views will tick right back up! You'll see!) The traditional working class, in his mind, is made up of obsolete mayonnaise ghouls who deserve to be driven to extinction.
It may also give him a sense of superiority- yes, he's of the working class, but he's also an intellectual, which means he's superior to the rest of those blue-collar Starbucks baristas (probably because he understands that if he was forced to debate a real intellectual, his opponent would mop the floor with him.)
I get some people find this aspect of Cinema Robert infuriating, but this is part of what makes him so hilarious to me- the absolute disconnect between his views and reality. He insists he's a blue collar worker, when in reality he's a lazy YouTube has-been. He believes that he's creative when in actuality all of his ideas are rehashes of ideas that came before (and not even recently; all are from his own youth). He insists that he's an intellectual, and yet can't view the world beyond the lens of pop culture, TV shows, movies, cartoons, and video games. He claims a quadruple helping of McBurgers is small for the average person, when in reality a normal person would be sick about halfway through. He insists he has the influence and reach he once had, yet his new Twitter account and declining YouTube views tell a radically different story.
He constantly insists he's something he's not, that the world is something it isn't, and that his Superior Future totally isn't a call for purging anyone who doesn't blindly vote blue. That he's so utterly divorced from harsh reality is how he got a thread with 2600+ pages (as of this post) in about 5 an a half years (or about 39.4 pages a month.)
I wish you a long life of amusing me, Bob! May your clogged heart never give out!
Edited for clarity