For C, obeying #7 is not even that difficult. It's much more of a challenge in C++ and probably Rust (and other languages).

> 7 Thou shalt study thy libraries and strive not to reinvent them without cause, that thy code may be short and readable and thy days pleasant and productive.

> Numberless are the unwashed heathen who scorn their libraries on various silly and spurious grounds, such as blind worship of the Little Tin God (also known as ``Efficiency''). While it is true that some features of the C libraries were ill-advised, by and large it is better and cheaper to use the works of others than to persist in re-inventing the square wheel. But thou should take the greatest of care to understand what thy libraries promise, and what they do not, lest thou rely on facilities that may vanish from under thy feet in future.

I'm not sure I follow. Why this would be difficult in any language with a usable package manager and a reasonable ecosystem?

Most people don't even know what's available to them in the standard library of C++ and under-use things in it. Especially STL algorithms but not just that.