It is also a conceptual question: to whom "belongs" a deleted document in a DMS?
Strictly speaking, since the document may be needed by anyone with access rights to it, it should also appear in recycle bins of all such users. However, such audience is way too broad and would only confuse users that are used to a recycle bin function from operating systems.
The other straightforward alternative is to place deleted documents into the recycle bin of user that deleted it, however this does not help other users that may need the deleted document, nor they know whom to contact to get the document restored.
What remains as viable option for the product is to provide recycling bin as an administrative function and as Martin wrote, to allow customization in case some other behavior is desired in a project.