Why do people use OpenSSL? Or any other library that forked from it
Why not start from a clean slate? Companies like Google could afford it
Security certifications are one reason. OpenSSL maintains a module for FIPS compliance, which includes an entire boatload of weak and broken algorithms nobody else bothers with.
Because as horrible as the OpenSSL code is, the best available clean implementation would mean using a language that's weird and French.
AWS actually has two libraries they use instead: s2n and aws-lc https://github.com/aws/s2n-tls https://github.com/aws/aws-lc