I think it comes down to that emacs itself has facilities for managing the background processes, and eshell in general tends to defer back to the surrounding ed

I think it comes down to that emacs itself has facilities for managing the background processes, and eshell in general tends to defer back to the surrounding editor for a lot of functionality. So if there's an "emacs" way of doing things, generally eshell delegates to that, instead of rolling its own.