The ability for one window to float over another was a later innovation and is of course more difficult to implement. The earliest versions of Windows were also tiling only, which is thus the traditional way.
https://www.lifewire.com/thmb/4_wxRAsOvukqwxpkQ-2SAZTx4ro=/2...
2.0 added floating windows
https://www.lifewire.com/thmb/qXTZ7Mk9cLKSc3wpEP2wK14oT8I=/1...
Note there's a big trend of making fullscreen applications. Skype acts like you bought a computer just to run it. Slack wants it all. Gmail is crammed with icons and features and can't deal with half width screen. Media players have notions, they call your computer a library.
Instead, many applications subdivide themselves into smaller windows - for example IDEs.
It's as if people gave up arranging application windows. They alt-tab (switch) between fullscreen apps. Moving windows around is usually too much hassle. Unless you drag and drop some files from one folder to another, but even then many people prefer copy/paste.
I find it funny, because I would say I have seen more floating window manager, when I was browsing GitHub, so I assume it is also quite easy to create a new one from scratch. Such floating VMs usually have 200-1000 LOC and die after 1 month after initial commit. Recently, xwm has been on HN [0] and it is small in terms of SLOC. There is smaller one called tinywm[1]. When we would compare them to i3[2] and sway, we can see they have thousand times larger codebase but they also bring a lot more features.
I keep my fingers crossed for more sophisticated WMs like PaperWM[3], which is "tiled scrollable window manager" to take off. They might synthesize ideas from floating and tiling managers and provide a better tool to manage windows on a screen.
[0]: https://github.com/mcpcpc/xwm
That is because the X11 server handles the drawing of windows over each other.
Older display protocols simply had no support for it.
No, why should they? Traditional mainly means what is established custom, not just what comes first or later. Floating Window Managment is around for decades, since the earliest generations of GUIs and everyone is using them today by default. Tilling back in the early days was a neccesarity, not a choice, and it was replaced fast, making it the loser of development. Later development made it a viable alternative to floating, but at this point floating was already dominating.
> The ability for one window to float over another was a later innovation
Kinda questionable. It seems MacOS had floating from the beginning. Windows was missing it in the first version, but added it in the second. But nur sure how widley used Windows was used at that time.
The Xerox Alto was the first GUI, and it used floating windows.