I agree. In fact, many open source (and closed source) codebases are understood by only a handful of developers with deep understanding of the design and code (

I agree. In fact, many open source (and closed source) codebases are understood by only a handful of developers with deep understanding of the design and code (e.g. the original developer or a developer with many contributions). The rest of us (including me) have a superficial understanding of the code at best. There's even a word that developers use to describe popular open source frameworks: 'magic'. A euphemistic way to say: 'I have no-idea how the code fit together, but this code library or framework is popular and it all works'.