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systemd has been a complete, utter, unmitigated success
(blog.tjll.net)
This is a most excellent place for technology news and articles.
Not specifically about systemd, but some things can't be backwards compatible because they might want to just do things different.
Nobody was forced to change, the distros saw the options and decided in favor of systemd, the same they decide a million other things.
Red hat dominated the market and pushed it on out. You must remember this, don't you?
I'd encourage you to go read the discussions Arch Linux and Debian had before deciding to go with systemd
Edit: fix grammar