Our code for sending stuff to CT logs is fully open source. But that's the tiniest slice of our compliance regime -- the vast majority of it is things like audit logging certain events, preserving audit logs in specific ways for certain amounts of time, ensuring dual-controls on all systems, being both audited and penetration tested annually, maintaining firewalls and vulnerability scanning tools, etc.

It's absolutely possible to spin up another new CA; lots of folks have done so over the years. But having time, and money, and prior experience all help a lot.