One need only look at Soloman's posting history on this site to see why he was the right person to lead Docker during its inception and the wrong person to lead Docker long term. It was clear in the discussions over Docker that Soloman was passionate about the technology he'd created and had a very particular vision for its future, which was often at odds with the way that posters here saw Docker and wanted it to evolve. But Soloman seemed to lack the ability to be diplomatic about it and showed some poor judgment in what he said publicly. That led to quite a few public spats that reflected poorly on Docker.

It's absolutely true that some people can evolve from a leader of a small company/team/project into a leader for a much larger one. But it's also absolutely true that not everyone can and that the skills to lead that larger endeavor are significantly different from the skills needed to get something off the ground. It's likely that Docker would never have gotten off the ground without someone like Soloman to take a very opinionated stance and drag people towards his vision. But if Docker is to continue to succeed, it now needs to expand its reach learn to be what people need rather than convincing people that they need Docker. Not being on the inside, I can't say for sure whether Soloman is capable of evolving into a leader that can move Docker in this direction, but the superficial view from the outside suggests to me that this was probably the right decision. It's no knock against him as either a leader or a technologist, it just feels like it's not the best fit going forward and his efforts would be better spent on something new that pushes a new vision forward.