And it's mainly because of Jekyll-Assets. It's just too useful for not only bundling assets but effortlessly md5 tagging everything for caching on the nginx side of things.
Hugo and others have nothing like this, and rolling your own set up isn't feasible for that because for it to be done right, it needs to be supported at the generator / plugin level so your template helpers know how to deal with looking things up from the untagged file name.
My site has about 170 blog posts and dozens of other pages and Jekyll's incremental reloader refreshes in a little over 2 seconds. That's about 1 second longer than I'd like to see a blog post get live reloaded in development, but it's good enough.