In that direction, it's usually going to be about robustness -- more tooling, less edge cases, a wider developer base, built-in cloud support, and so forth. The more popular a database is, the easier just everything is.

Occasionally it's going to be some very specific aspect of performance limits, or a feature like spatial indexes that work in a special way. And occasionally it's going to be about cost or better integration with a particular cloud or other specific piece of tooling.