“We’ve all heard this riddle: if you dig down deep enough in Windows 10, you’ll find elements that date from Windows 3.x days.”
Fluent Design sits on top of Metro, which sits on top of Windows 7’s ribbon, which sits on top of dialogs from Windows 95 and earlier. Microsoft starts a new design language every few years and never finishes moving the old screens over. Even its plan to retire classic Paint got reversed after a backlash. Windows 10 is a museum with a new lobby.