Final answer:
The CIOs began reporting to hospital CEOs in the 1990s as their roles expanded due to the technological revolution and increased complexity in healthcare management, necessitating closer alignment with top leadership.
Step-by-step explanation:
The most likely reason that Chief Information Officers (CIOs) began to report directly to the CEOs of hospitals in the 1990s is due to the broadening role of the CIO. The technological revolution of the 1990s, coupled with the healthcare sector's move towards a mass production and efficiency model, required hospitals to adopt new information systems. These systems were critical in managing the increased demand on healthcare services and the consolidation of providers. As a result, the CIO's role expanded significantly to include the integration and management of these complex, technologically-driven systems, justifying a direct reporting line to the hospital CEO.