Introduced the modern tabbed interface, making it easier to switch between floor plans and 3D views.
Many large-scale infrastructure and architectural projects stay in the version they were started in to avoid data migration risks. Revit 2019 was a milestone release that introduced several "quality of life" features we now take for granted. Key Features You Should Be Using: Search results for revit 2019 (19)
Since Revit 2019 is now an "Obsolete Version" in the eyes of Autodesk: Introduced the modern tabbed interface, making it easier