s2n != OpenSSL
s2n is a library that implements <stuff>. OpenSSL is an entire suite of apps and libraries that implements <lots of stuff>. They are not directly comparable.
For example I doubt that you will find a binary in s2n for generating an entire PKI thingie. How do you use it to create a CA, inter-CA and then various certs? No, it doesn't.
OpenSSL is not perfect but it has the benefit of having gone and is going through the mill and like all other systems, sub systems and apps has been found wanting and has patched flaws when found.
Apples != Physalis - shock.
(Sorry, forgot to include a suitable icon)