This does not take into account the value of contribution to these projects by external contributors. One of the main selling point of OSS is the collaboration

This does not take into account the value of contribution to these projects by external contributors. One of the main selling point of OSS is the collaboration value. If you develop a software for your needs, but the software in itself is just a tool and not your core business, you can share the cost of developing it with thousands of other individuals and companies.