Since 2011, almost every year, the WordPress team have released a new theme.
However, the team didn't release a theme for 2018 because there were no major WordPress releases.
This year, we're back on track and there's a new default theme, called "Twenty Nineteen". This new theme is needed to take full advantage of this flexibility offered by Gutenberg.
Twenty Nineteen offers significant creative freedom. However, it’s almost a blank slate to begin with, and that can be a little daunting.