Which is exactly why if you aren’t a database vendor, you shouldn’t have your engineers spend their time maintaining a proprietary database technology.

If you maintaining a proprietary database technology solves a problem that provides some shareholder value, then go ahead and do it.

Maintaining off the shelf software that you got from Github provides no shareholder value whatsoever, however. It is a pure cost center.

As a CTO you do not want to be the guy that runs a pure cost center department.

There is negative value in rebuilding things that could have been downloaded for free from the internet. Postgres, MySql, Sqlite, RabbitMQ, Redis, Kafka and all the other common tools each have had thousands upon thousands of hours sunk into bugfixes, correctness guarantees and performance work. Rebuilding a poor version of that does not provide shareholder value at all.

Many others have said this elsewhere in this thread, but the cost of using all those things is not free. Every added service is an extra burden to maintain, all the way from writing code through to running and maintained in production.

Sometimes, the cost (both immediately and long term) of introducing a new component into your stack will exceed the cost of building and maintaining an inferior in-house solution, and sometimes it won't. Either way, the cost of these freely downloadable services is not just their cost to download.