Tossing everything into a single file is not required. You can use includes to have "a single file to add to the project", and still split your code in smaller

Tossing everything into a single file is not required. You can use includes to have "a single file to add to the project", and still split your code in smaller, readable files. See https://github.com/jedisct1/libhydrogen https://github.com/jedisct1/libhydrogen for example. It's a single-file crypto library from an application perspective, but everything was not stored into a single, hard-to-navigate file.