It's the same deal with Debian and systemd. It's not the init system. It's the thing it represents. Having to either adopt systemd or run GNOME in an unsupported configuration seems like a clear-cut choice (which is why systemd is now the Debian default), but having a major upstream force you to significantly rearchitect the distribution seems like a pretty significant loss of control. This is at the same time as other upstreams have gradually ripped control out of the hands of Debian developers in other ways: Firefox, librsvg, and python-cryptography adopting Rust suddenly made it a lot harder to support a bunch of niche CPU architectures. Speaking of Rust, and also Go, they use static linking and have their own library package managers, which both makes it harder for Debian to package and simultaneously easier for users to install a binary directly provided by upstream. And languages that don't have static linking support can always use Docker.
Honesty, I wouldn't want to be a Debian developer right now. Red Hat has tried to reinvent themselves in a world of containers, but since Debian is a volunteer organization and not a corporation, it's a lot harder to pivot (attempting to pivot would probably cause all their existing volunteers to quit, while failing to attract new ones). What sort of future does Debian even have, if they have no decision-making power over the core OS, and all the applications route around them?