There are a number of reasons why code or documentation contributions may not be adopted by the OpenSSL maintainers.
With documentation there is another factor. People rely on documentation as showing the preferred way of using the software, and once documented an API it effectively "cast in stone" for future versions of OpenSSL. There is a reluctance to document features that may not yet be in a final form.
With OpenSSL there is usually a preferred general high-level API (EVP) and then many lower level function calls that can be used to achieve similar outcomes. The higher level abstractions are usually the best solution for all common application requirements. As a result there is a reluctance to adopt and publish documentation of low level APIs when the corresponding preferred high level approach is not yet adequately documented.