You can get high availability without a "distibuted system", just an active/passive failover cluster may be enough for some requirements. Even failover (sometimes seamless) on a VMWare cluster can help with planned maintenance scenarios without downtime, etc.
Another way of achieving HA together with satisfying disaster recovery requirements is replication (either app level or database log replication, etc). So, no distributed system is necessary unless, you have legit scaling requirements.
If you work on ERP-like databases for traditional Fortune 500-like companies, few people run such "sacred monolith" applications on modern distributed NoSQL databases, it's all Oracle, MSSQL or some Postgres nowadays. Data warehouses used to be all Oracle, Teradata too - although these DBs support some cluster scale-out, they're still "sacred monoliths" from a different era (they are still doing - what they were designed for - very well). Now of course Snowflake, BigQuery, etc are taking over the DW/analytics world for new greenfield projects, existing systems usually stay as they are due to lock-in & extremely high cost of rewriting decades of existing reports and apps.
Another way of achieving HA together with satisfying disaster recovery requirements is replication (either app level or database log replication, etc). So, no distributed system is necessary unless, you have legit scaling requirements.
If you work on ERP-like databases for traditional Fortune 500-like companies, few people run such "sacred monolith" applications on modern distributed NoSQL databases, it's all Oracle, MSSQL or some Postgres nowadays. Data warehouses used to be all Oracle, Teradata too - although these DBs support some cluster scale-out, they're still "sacred monoliths" from a different era (they are still doing - what they were designed for - very well). Now of course Snowflake, BigQuery, etc are taking over the DW/analytics world for new greenfield projects, existing systems usually stay as they are due to lock-in & extremely high cost of rewriting decades of existing reports and apps.