While IBM has never been the best and the brightest in the world of technology, they have always been a reliable investment, performing year after year and decade after decade. Even as new companies come and go and corporations battle each other into bankruptcy, IBM products still scan merchandise at stores, run the technology that handles the checkout lines, handles the shipping routes that manage the delivery trucks, operates the warehouses that process the goods, operates the factories that make the goods, and sits in the offices of the salespeople who arrange to have the goods sold in the stores. It is never the leader in technology in any given market, but it always has a market share.
IBM products never stand out as 'modern', and most people think of them as laughably out of date when they see them. The fact is, though, IBM tech lasts. It's built tough, simple, and without many things to go wrong. IBM continues to make new products, and doesn't seem to be going away anytime soon, regardless of what other markets do.
IBM products often find their way into the corporate environment because they retain their value for a very long time. IBM products are almost never cutting-edge, but almost always rugged to some extent, often to the point of ridiculousness; an IBM cash register once took several shots from a handgun during a failed convenience store robbery and still remained functional for the remainder of the shift and several days afterwards until it was brought in for aesthetic repairs. IBM touch displays can withstand blows that would crack most unprotected peripherals, and IBM scanners can survive drops that would ruin most other devices.
IBM sells a variety of electronics and machinery targeting the medium to large business markets, with outdated but still functional IBM products often trickling down into less affluent hands over time as larger businesses update and sell off their old inventory on the cheap.