I guess you have never compiled a Linux/BSD distribution from scratch and supported it alongside its infrastructure and lead its maintenance process.
Even without that, if you want downloadable and runnable software platforms, look to public Git repositories. Some of the people who have no financial motivation will release what they do alongside installation procedures and quality of life scripts and architecture documentation.
Most of the open source platforms doesn't publish this documentation and doesn't make installation easy to keep a sizeable moat and protect the platform they have developed, hence this is why we have a division between "Free Software" and "Open Source".
In short, "The bulk of really valuable commercial code" is self contained, but not open source, or if open source it's not Free Software and made deployable for other parties. Otherwise it loses monetary value in the eyes of the people who develop that for the monies.
Otherwise we have have Elasticsearch incident, where they pivot and move to "Source Available" model to protect their castle.
