Sqlite3 is present in the default installation of most Linux distributions. It has proven itself from years of battle testing in many different environments. To use DuckDB or LevelDB would probably require pulling in an additional dependency.

Neither DuckDB nor LevelDB existed when journald was created. Not to say it couldn't be done today, but just some historical context.

No duckdb (or parquet). If you want to avoid writes and write amplification, you really want to avoid re-writing all 122880 rows of a row group every time a single insert happens.