As VMware is getting considerably more expensive it's reasonable to assume some CEOs are aware of that. It would be enough if one or two of them for one reason for another googled "cheap virtualization" or talked to some "tech guy" and somehow "Linux is cheap/free and can do virtualization" is what stuck with them. Then they talk to their friends at the golf club and after a while the topic reaches critical mass in those circles and spreads across those companies, probably not without playing "Chinese whispers" along the way.