Because they do more harm than good. Every year we get the same issues, when the new Ruby version is released on Christmas: All the fat binary gems are incompatible.

This is although I release a new version of rake-compiler-dock at the same time as well as several core libraries (ffi, nokogiri, pg) with support for the new Ruby release. It still takes months or even years until other important libraries get updated and the new Ruby version gets usable on Windows.

Years ago I added gem version constraints for fat binary gems to rake-compiler, so that rubygems or bundler could solve this issue by switching to the source gem automatically. Unfortunately this doesn't work, since bundler still doesn't support this use case. Therefore Windows users have to use the various workarounds mentioned in all the issues (#142, #149, #139, etc).

Another issue is that fat binary gems hinder to run and test applications or gems on Ruby head versions, since they can't support ruby-trunk by design.

bcrypt-ruby doesn't depend on any external libraries to be available, so that it builds fine with any older or newer RubyInstaller version. It's easier than ever to install the Devkit on Windows and the Ruby+Devkit flavor is by far the most downloaded version. So there's no need to provide fat binary gems for Windows.

Please make Windows a first class citizen by dropping the x64-mingw32 and x86-mingw32 gem versions!