Or Windows. Windows isn't even 100% consistent in style in regards to what you get out of the box, with multiple generations of old stuff always poking out somewhere.
And even MS apps have long invented their own UI -- Office has long brought its own particular controls. And the moment you install almost anything, any semblance of consistency goes out of the window.
At least GTK and KDE are two common, polished styles. For a long time it was a fashion for every random app, including technical things like antiviruses to have some sort of goofy, customized UI toolkit with irregular shaped windows. (https://i.imgur.com/P3Vu11W.jpeg)
Funny how even that goofy shield has retained a dedicated and distinct title bar with window controls that looked almost like all the other title bars.
And even MS apps have long invented their own UI -- Office has long brought its own particular controls. And the moment you install almost anything, any semblance of consistency goes out of the window.
At least GTK and KDE are two common, polished styles. For a long time it was a fashion for every random app, including technical things like antiviruses to have some sort of goofy, customized UI toolkit with irregular shaped windows. (https://i.imgur.com/P3Vu11W.jpeg)