How is data loss possible if we lose primary in Read-Scale (clusterless) AG Sync-commit configuration (SQL Server AlwayOn)?

Question

Microsoft documentation for Read-Scale (clusterless) failover: "If the primary replica is not available and can't immediately be recovered, then you need to force a failover to the secondary replica with data loss."

https://learn.microsoft.com/en-us/sql/database-engine/availability-groups/windows/configure-read-scale-availability-groups?view=sql-server-ver16

Question: How is data loss possible after failover if we have sync-commit mode configured and primary becomes unavailable? Databases are SYNCHRONIZED before failover.