I'm definitely not saying it's not a good idea to read code—it's just something that almost nobody does, because, as you've said, it's very hard work; much harder than having the "story of the code" told to you in a book or a blog post.

It's also work no one knows you did; unlike reading a book or a blog post, you can't really reference or quote a codebase to prove you know what you're talking about, because you can't expect the people you're talking to to have read the same exact lines.