Reason: I’m using (& pushing) Nix(OS) passionately and was quite “dissatisfied” (to say to least) with the development in recent times, not only over the last few weeks. I’m heavily invested in Rust, using it for my own projects as well as part of $dayjob.
The most important part though - for me - is that I’m really, really care about free software and taking a strong ethic stance on that topic. Proprietary software is always a downgrade.
Experience: I’ve been writing software in Rust for about 6+ years, professionally for 3+ years, everything from bare-metal to large web/API backends. As for Nix/NixOS/nixpkgs, I’ve been using Nix for nearly 2 years now and 1 year being a nixpkgs maintainer, having contributed throughout the entire stack (see also this list for reference).