Csv export in drill down

I don't think there is, unfortunately, at least not from the UI. You might want to log that in IdeaStream.

For the record, it can be done with a business rule, in a couple of different ways:

• Using Brapi.Import.Data.ExportStageData; there is a Snippet showing how to use that, as well as a working Extender in XFR_ExportStageData in Golfstream. By default it reasons in terms of workflow unit, but you can filter down the records using extra conditions (e.g. "U1 = 'My Product' ") passed in a List as the FilterExpressions parameter. You then execute the extender from a Data Management step.
• Using StageRelationalBlendHelper.GetStageBlendDataTable. This is documented in the "Relational Blending API" section of the Design and Reference Guide. It allows you to retrieve Stage records by scenario, entity, time, and account, resulting in a DataTable object, so if you need more fine-grained filtering you'll then need to loop through the rows of that table. Again this can be executed in an Extender from Data Management.

If you need to export large amounts of drilldown records on a regular basis, I would strongly recommend writing an extender and scheduling it with Data Management - the initial effort will pay off by saving busywork in the following months. The DrillDown UI is largely meant for interactive use and quick analysis on an ad-hoc basis.