MsSql Bulk Insert With commit size 1 vs Simple Insert
Singleton inserts via a bulk insert technique are significantly slower than normal singleton inserts.  To prepare for bulk inserts, the client API must first send column meta data describing the tabular data stream that follows, a task not needed with normal inserts.  This overhead is offset by improved performance when streaming multiple rows of data but not when single rows are passed.  See https://msdn.microsoft.com/en-us/library/dd304523.aspx for details of the TDS protocol specification.

I ran tests a few years ago for a presentation on insert performance and found single-row bulk insert performance using SqlBulkCopy averaged about 500 rows per second compared to 1,800 per second for inserts.  With 100 row batches, bulk inserts averaged over 10K/sec compared to 3.5K with single-threaded singleton inserts. I would expect a similar difference with the IRowsetFastLoad OLE DB interface commonly used in SSIS.