I think people get hung up on high availability (HA), and ironically don't test their backups. Single node with streaming backups to S3 (simple in a single writer system) can give you a system that will at most lose a few seconds of data (interestingly RDS has a 5 minute window of dataloss).
Multi node systems tend to have more failure modes, so fail more often, high availability is not free.
If you replicate data between two nodes (that are note async backups). You have to maintain strong data consistency. So writes to the database are considered successful only if the data is written to both nodes. If either node became unavailable you'd be unable to write anything without sacrificing consistency, reducing our overall availability rather than improving it. Also increasing latency.
This is why the whole multi node HA push by the industry is so laughable. A lot of time it makes systems more fragile.
