QuestDB engineer here: We use jlink to create images for selected platforms. This means not even JRE is a dependency: You unpack a tarball and you are good to go. See: https://questdb.io/docs/get-started/binaries/
Keep in mind the JNI libs are platform specific. That means available platforms are a function of what the JRE runs on AND they have built the shared lib for (and bundled in to the jar)
The only thing they say that explains it is they end up with a single jar file, whose only dependency is the JRE.
So I guess they get platform independence and easy installation.