I waited for PiP or as Windows calls it make a Window always stay on top (like Win and Linux can do for decades) for so long and now I have to use Safari as it

I waited for PiP or as Windows calls it make a Window always stay on top (like Win and Linux can do for decades) for so long and now I have to use Safari as it seems to get it working. I also doubt it will work with Flash or any live web sport streams :( What was/is so complicated to get an always on top window on OS X aka macOS?