The problem is that unix, and more generally any operating system, is fundamentally flawed with respect to security and reproducibility. It's nontrivial to inspect these installations for vulnerabilities because there is nothing that specifies the precise set of software that is in that installation. Some stuff is compiled from source, some stuff is installed via one or more package managers, each of which may bundle additional software that one may not know about if they didn't inspect each piece of software carefully. Furthermore, one cannot even verify the installation reasonably because the results are different depending on when it was installed.
In short, operating systems are insecure by design.