The best marketing I can think of would be native Windows support. On the 2020 Stack Overflow survey, developers are 45% on Windows compared to 27% on Mac and 25% on Linux. I realize tools like WSL are available, but those workarounds can be awkward.
In addition to the individual developers who would use Nix, I think upstream projects would be more likely to use Nix as their main packaging tool if it natively supported most of their users.