I suspect that Ruby also benefited from having a comparatively young community. There are folks that used Ruby before Rails, but the majority of Rubyists only started in 2006 or later, so they are used to the faster replacement rate of modern Open Source and didn't have so many legacy codebases to worry about.
As I understand it, Matz considers the upgrade strategy until now quite successful, mostly because at the same time breaking changes occurred people got things they wanted (e.g. faster VM) which encouraged them to upgrade.
Hence the "ruby 3 will be 3 times faster than ruby 2" idea, that's the carrot that should contrast people's will to not update.