That's only true if you discount or ignore the time cost of requiring an internal engineer to manage those open source systems. A lot of the reason to use exter

That's only true if you discount or ignore the time cost of requiring an internal engineer to manage those open source systems. A lot of the reason to use external services is to mitigate the operational cost (which can be amortized across all the service's customers), since presumably that systems isn't a core competitive advantage for the company.