That's absolutely true. However, most systems that think they need scale-out are either worrying about a problem they don't have yet, suffering performance problems due to poor database design, or have not fully explored logical (dynamic or hash-based) sharding as a solution to their problems.
A huge proportion of modern software businesses can run on single-writer RDBMS instances, properly engineered, at a fraction of the operational and implementation cost of a scale-out solution. That applies to hosted and self-managed solutions equally, in my experience.
Sure, but scale isn't everything. Operations are far more important, especially when you're a small team.
Modern distributed databases scale better but also have better replication, high-availability with automatic failover and no downtime, easier upgrades, easier backups, and generally less maintenance. Removing the single-point of failure with efficient distribution while being able to run easily on docker/kubernetes makes a big difference over a single monolithic database server.
The desire is generally for high availability now and ability to scale out in the future; while a single write db is generally more than enough performance wise, it doesn't give you high availability which is the main desire.
A huge proportion of modern software businesses can run on single-writer RDBMS instances, properly engineered, at a fraction of the operational and implementation cost of a scale-out solution. That applies to hosted and self-managed solutions equally, in my experience.