Often open sourcing a project requires a lot of work. If it uses licensed technology it may require some money too. And sometimes the engineering is uniquely tuned to the context in which the project was developed to the point that it makes no sense, for example the code contains dependencies on specific service providers like hosting companies or CDN's or expects unique hardware configurations.

Surely there is value in code that can't be run. If I write a nodejs app that only runs on Google app engine, it still might be useful to someone else.

I think you underestimate the difficulty of open sourcing some projects.

At the last company I worked at, we really wanted to open source some of the stuff we were doing, but we literally couldn't because we depended on some private APIs and were under NDA.