I would imagine it’s because that’s a developer decision, not a report viewer decision. Interactive mode gives report viewers some options to rearrange the report (add remove objects, add/remove filters, sorts, and so on) but the merge dimension setting is part of the report architecture and should be done by the report developer only.
Thanks Dave. What I am asking is that end users have only interactive viewer for creating and editing reports available and in a specific report, developed using interactive viewer where is the option to have all rows from one query and matching from the other while merging (similar to merge dimension in java panel).