For tailwind the devs apparently were able to solve the long build time by using a modified library (@tailwindcss/jit - npm).
https://discourse.roots.io/t/sage-10-browsersync-issue-with-reload/20314/26?u=strarsis
Node-sass has been deprecated in favor of Dart sass, which is now the reference implementation.
However, uncompiled, JavaScript Dart sass seems to be slower than a compiled binary (from what I read).
So maybe this is the underlying reason?
https://github.com/sass/dart-sass/issues/206
https://github.com/sass/dart-sass/issues/248
https://github.com/sass/dart-sass-embedded