Why does everyone run ancient Postgres versions?

Because the actual process of upgrading Postgres is terrible.

I say this as someone who absolutely loves using it, but the actual process of upgrading Postgres is something that takes significant downtime, is error-prone and you're often better off just dumping all the databases and reimporting them in a new folder. (A good idea in general since it'll vacuum and compact indexes as well if you do it, combining a few maintenance routines in your upgrade path.)

It requires having the previous version of Postgres installed, something which can mess with a number of distro policies (not to mention docker, which is the most popular way to deploy software that will typically rely on Postgres), and unlike most software with that issue, Postgres is software you want to be managed by your distro.

Therefore, most people only upgrade by necessity - when their distro forces the upgrade or the version they're using reaches EOL.

> Postgres is software you want to be managed by your distro.

Why?

For production systems I generally try to avoid using anything not built internally. When it comes to PostgreSQL, for example, if you want to submit benchmarks, or you want to report bugs, an important or sometimes a mandatory component is to provide compilation flags. Also, seeing how every kind of storage can act in a different way, tuning of higher-level storage programs seems inevitable. Even though PostgreSQL has a lot of configurations that can be done to the compiled program, some (eg. block size) are compile-time that can only be changed by compiling the program.

> if you want to submit benchmarks, or you want to report bugs, an important or sometimes a mandatory component is to provide compilation flags

On all open-source distros, you can look into your distro's source and check their compile flags.