After Stripping With Archive Manager The Exchange Database Is Not Shrinking in Size
Although Archive Manager is able to strip out the bulk of the size of the messages and attachments in Exchange, this will not reduce the overall size of the Exchange Database.
The size of the database hasn't changed there is just some space within the database.
This "white space" will be used by Exchange first, before expanding the database any larger.
Event ID 1221 in Exchange will report each day when the Online Defrag in Exchange is run just how much White Space is available to be purged from the database.
This blank section of your database can only be realized
The following KB from Microsoft details how to free up this space: