That's right, but we've plenty of "plumbing" software for the Linux ecosystem whithout funding companies behind, and they get regular contributions.
The same should happen with the init system. Of course, it's different when the software pretends not just to be an init system but also a replacement for tons of other daemons like cron, inetd, networking, etc, making it a huge piece of software. But maybe that's the problem in the first place.
The point there is that most of the underlying user space plumbing of modern Linux system is in fact funded by Red Hat in one way or another.
(And in this context it is probably useful to realize that on the kernel side of things the amount of funding from Red Hat and IBM is comparable)
Similarly, having something worth switching to also depends on labor to develop such an alternative. Upstart is no longer funded, and was the closest (including in terms of mindshare that caused people to spend labor developing integration between their software and the init system).