You know my hypothesis why, because they don't have side projects. They have silo'd themselves into whatever niche project or have been on maintenance mode on a piece of software for years and never evolve. Sometimes it's not their fault, their company has pigeon-holed them into whatever software and they can't escape for whatever reason.
They should have side projects (if they care to keep learning) or lest be left behind those in more dynamic companies or those that have side projects to evolve.