You're thinking of a different kind of company than the paper is talking about. (The headline, presumably written by the university's PR team, is a bit misleading about this.) The paper is about a certain kind of firm (e.g., the Big Four accounting firms, management consultancies like McKinsey, some elite law firms) that explicitly uses an "up or out" model, and explains why this kind of firm's business model (in particular, renting out the services of a particular employee to each customer) leads to this. The findings don't apply to other kinds of firms; e.g., in a typical big tech company, most engineers don't work primarily with a single customer, so the preconditions don't hold.