openssl claims to use /private/etc/ssl, but appears not to, What The Heck?
This issue is the result of a known bug in OpenSSL that was reported in February 2013 and tracked here (log in using username guest and password guest). At the time, the latest public release of OpenSSL was OpenSSL 1.0.2. The issue was marked resolved in October 2016, and the bug no longer exists in releases after this date, the earliest of which is OpenSSL 1.1.1. Some users have reported that the bug was also not present in "version 1.1", to which they may be referring to OpenSSL 1.1.0 or forks of it — I have not confirmed whether the bug exists in OpenSSL 1.1.0.

The openssl binary included with macOS is LibreSSL, which is a fork of OpenSSL that originated from OpenSSL 1.0.1g. Since the bug existed in that version of OpenSSL, it persisted in LibreSSL until it was noticed and fixed by their developers, which was somewhere between the version you're using (LibreSSL 2.2.7) and the version I'm using (LibreSSL 2.8.3, which is packaged with macOS Catalina).