Why does discussion always have to devolve into this? This isn't an advertisement asking brand-new greenfield projects to base their work on C libraries. This work is done because it's an update to nghttp2 to add support for HTTP/3. The reason you would use it is because you're already using nghttp2 and want to know about the added features. The list of tooling using nghttp2 is pretty extensive, including at bare minimum the Apache web server and curl, which collectively likely initiate at least a plurality of the Internet's HTTP traffic because of their age and ubiquity.

Why are these tools written in C? Because they're old. nghttp2 was released in 2009, before Go was released and before Rust was even a twinkle in its eventual creators' eyes. Adding comments like this any time a feature announcement to a C library is made comes across like you're saying nobody should ever update tools that are already in use. Should Linux just stop doing work until the kernel is rewritten from the ground up in Rust? Should all longstanding software take a five-year pause to do total from-scratch rewrites? Can you see why that is impractical? If you can, then you can see why libraries like nghttp2 exist and continue to add features.