It's always such a bizarre experience when people advocate for centralized repositories for Windows. Windows, unlike Linux, comes in very few flavours/versions (and with decent backwards-compatibility story), so the application developers can very well be (and in practice, well, are) expected to build the apps for the Windows versions they care about and then use their web-sites to distribute it.
In this case with iPerf3 we just have a sad story of two forks, and the group that owns the namesaked website for some reason could not be bothered after 2016 to re-upload the releases of the other group. Well, similar things happens in "official" Linux distros as well, with severely outdated packages.