なぜ rbenv(ruby-build) は Homebrew の OpenSSL を使わないの?
こちらのマージ済み PR に理由が書いてあります
ruby-build already does a lot of work to make sure that the version of ruby you're installing has the correct version of openssl also installed. Looking for any version of openssl installed by Homebrew is problematic for a few reasons:
* The user may have an incompatible version installed
* The user may not know that a particular version of openssl has been installed by Homebrew
* The openssl version split now makes this logic more difficult to maintain for all versions of ruby that ruby-build can install
Let's stop looking for any version of Homebrew's openssl by default so that the user always gets a working version of the ruby they're installing. Advanced users can use the RUBY_CONFIGURE_OPTS="--with-openssl-dir=/my-openssl-directory" option if they don't want to install the ruby-build defined compatible version of openssl.
上記の PR は #general での hsbt さんからの情報をきっかけに見つけたものです。ありがとうございました!