Those people are all doing white collar jobs nobody does today: adding up columns of numbers with desktop adding machines, retyping manuscript memos, responding to customer and vendor mail, summarizing other hand-generated reports into newer more digestable reports (which are in turn the input for yet more manual clerical steps), maintaining paper indexes into warehouse-sized file stores, etc.
Each of these people (well, it's a movie, but the real people they represent) had a career, performance reviews, Christmas bonuses, all of it. Now the whole work output of this entire high-rise office building floor (and probably more floors on either side of it) can be replaced with one copy of Excel.
I'm confident we'll come up with all kinds of new data-pushing jobs to hand out, assuming we can contrive to continue living in conditions of energy abundance (like we already were in 1959).