I think it is quite obvious: SAS is looking for a cheap jack that is willing to operate an aircraft selected by SAS. If I am not mistaken, SAS has outsourced its own CRJ900s to Cimber Air and pitting Cityjet against Cimber with the same type makes good sense in the long run to keep costs down. If SAS would have demanded ERJ190, Cityjet would probably have ordered that type just as well.