The issue with systemd was that many people felt that it was pushed onto them while previously such things would just exist and got adopted slowly if people liked it and then actively adopted it. This model worked fine, e.g. there were many different window managers, editors, etc. and people just used what they liked. For init systems, distributions suddenly decided that only systemd is supported and left people who did not want it out in the cold. It is similar with Rust. It is not an offer, but something imposed onto people who have no interest in it (here: kernel maintainers).