As a counter-example, rethinkdb is open-source but the company failed and nobody cares about using it anymore. What would you do with that? Start building new database features yourself? Or just get your data out and move to a different system?
Databases are so lock-iny and critical that it's only natural for closed source database startups to be considered too risky to touch.
It's better to practice proper vendor management and weigh all the risks and realities instead. If you're not more capitalized and viable then your vendor, then you have more important things to worry about then your vendor disappearing overnight.
A real technical reason might be "the ability to fix the software ourselves" or "easier debugging of the software". Avoiding vendor lock-in isn't a technical decision
That hasn't been my experience, at least not on any suitable time scale.
I strongly suspect that the vast majority of those of us who have worked somewhere "not more capitalized and viable" than the vendor share that experience.
Even when a vendor's support engineer is fully capable of solving the problem, the sense of urgency can't reasonably be expected to match that of a much smaller customer facing potentially catastrophic data loss (or other existential-threat-level consequences).
I do not see how having spare engineering talent capable of reading, editing and running a custom database build is the more realistic or faster option for any business in case of issues.
Those are totally useless during an existential crisis without associated indemnity (which any vendor would be crazy to provide) against loss due to failur to perform.
> I do not see how having spare engineering talent capable of reading, editing and running a custom database build is the more realistic or faster option for any business in case of issues.
I don't see how it isn't, considering that "custom database build" could be so simple as to be trivial. In the GP's case, it was merely using a specific version.
Even the characterization of the required engineering talent as "spare" seems incongruous, as, in small companies, the talent requird to handle unexpected problems with technlogies fundamenta to running the business is essential, not superfluous.