Right, but IBM used to comprise almost the entire hardware and software market. Over time, they failed to consistently deliver the best experiences to consumers and clients, so they definitely declined from their glory days. I understand your comparison about real estate developers, but I don't think it applies here. IBM can buy competitors, but if they can't make sure their acquisitions remain the best in the market, then the acquisition loses profitability, or even becomes a writeoff.

As an anecdote, I used to work on one of their analytics products, which they acquired in one of their biggest acquisitions ever. Nevertheless, we were competing for clients with smaller, leaner, and sometimes better teams in the same field. We had no inherent advantage in development over our competitors either. Sure, IBM could always buy them, but then they'd have another x billion dollar investment to turn around, and still no way to stop new competitors from taking the clients, other than creating the best product - which would be net beneficial for society anyway. In many cases though, IBM's attempts to exert control by acquiring other companies backfired because they failed to provide client value, and the company has had to write off a lot of losses by trying.