...but they're not. Perhaps one time in 50 you'll find a topic so well worn that you have choices between multiple mature, stable libraries with good APIs that lets you dig into the source code to see how nice it is (by whatever metric) to decide if you want to use it.

Perhaps what, json parsers?

I can barely think of any other examples.

It's a completely pointless metric.

The beauty of the API is far more important than looking into the implementation to see how it was written.

Heck, the library could be one giant regex on one line, but if the api is:

    void *libfoo_random_meaningless_name(void *n, ...);

I very much doubt the elegance of the implementation is a metric that should be used to pick a library; there are far more important metrics to look at.