The cURL project consists of roughly 100 thousand lines of C code according to Ohloh. You do not have to when you choose a more modern safer language that can

The cURL project consists of roughly 100 thousand lines of C code according to Ohloh. You do not have to when you choose a more modern safer language that can export functions with C linkage and can trivially call C functions. You decide to use a new language and write new functionality or functions that have to be rewritten anyway. For instance, gcc first switched to g++ as the default compiler and started allowing a subset of C++. Firefox started using Rust here and there where/when it makes sense. There are countless other examples. I think very few folks would actually propose converting a 100KLOC or an MLOC project to another language. (Though Go did did it with their runtime and compiler :), though that's quite a special case).