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