Why can't disks be mounted or unmounted after creating a full machine snapshot of a cloud host?

A full machine snapshot creates a consistent snapshot of the cloud host's system disk and data disks at the same point in time. 

Mounting or unmounting data disks during or after snapshot creation will cause inconsistencies between the disk topology information stored in the snapshot and the current state of the virtual machine. After a full machine snapshot is created, the disk topology of the cloud host is locked to prevent snapshot data corruption caused by mount/unmount operations and guarantee the reliability of rollback operations.