Out of interest: Which init system is used on several OSes by default? Last I checked all OSes wanted init systems that made actual use of their unique kernel features. Any POSIX compliant init tool will by definition not support OS specific features out of the box. Maybe you can hack them on?
I see this "they depend on systemd-specific features": Of course. The systemd project listens when user space developers report the probpems they face with their problems and tries to solve them. Of course developers are going to use that, why would they want to hack around a problem poorly instead of using a proper solution that is more stable, robust and has seen way more testing than anything they could write themselves? The problem is not systemd here, its nobody else bothering to do something.