Lack of any obvious vision or ideas: a safe pair of hands. The similarities are there, and not just Sundar/Ballmer but Sundar/Ballmer/Cook. It seems visionary CEOs like to appoint non-visionary successors. Someone who won't make big changes to their baby.
This is often inherent in the organizational structure of big companies. To the extent that there are visionaries in a big company, they're usually not anywhere on the executive team, or even anywhere that the CEO comes in direct contact with. If they were, they'd clash with the CEO's vision, which first of all would be confusing and inefficient for the organization and second is a power contest the CEO would win. So if the board wants to appoint a visionary from within, they usually need to reach several levels down in the org hierarchy, to someone who's run an innovative division semi-independently but been protected from overall company politics. If they elevate this person to CEO, everyone above them in the org chart will quit, as they've now been passed over for the top job.