Brian Solis writes:
Businesses deploy new technology without designing goals, processes, and reward systems to promote new engagement. Additionally, decision makers miss the need to empower key stakeholders to drive adoption and address internal skeptics and detractors. ... Everything begins with investing in a culture ... Tools only take you so far. It’s the philosophy and eventually vision and leadership behind the implementation that serves as the foundation for internal engagement.
Solis was considering the need for leadership in implementing social networking "behind the firewall", but the remarks about what is needed identify the reason that this, and many other technologies, have failed to achieve results.
Whether it's a social network, a knowledge management system, or a new spreadsheet application, it doesn't catch on if it's installed and ignored. But even at that, you're pushing a rope uphill if the culture isn't right before the tool is purchased.