Worse is better. C and Unix were faster to implement new stuff as they were only 'good enough'. Lisp machines wanted to do everything 'right', right from the start, and were slower to implement new features. Unix was already winning by then...
Another big open source DB I'd like to hear about more often is Firebird (https://firebirdsql.org/) which was forked from the Interbase code released by Borland (don't remember how they were called at the time). Four choices of connection model (process-by-connection, thread-by-connection, some weird mix, and in-process), full ANSI SQL, runs on all major platforms, and uses single file databases. Seems to be the best of SQLite (inmem, single file), MySQL (lots of connections fast) and Postgres (standard, robust) to me, in a single package. But for whatever reason it seems to be completely off the radar on HN...
Once again, nothing.