By Microsoft design, graphic images are not supported in Excel 2003 XML Spreadsheet Markup Language. Since this is the form of the output written by ODS TAGSETS.EXCELXP (Excel 2003 XML), that means that other ODS destinations, like ODS HTML, ODS RTF, ODS PDF will show preimage graphics, but ODS TAGSETS.EXCELXP output will not use the PREIMAGE file. In fact, if you had tried PROC GPLOT, inside your TAGSETS.EXCELXP "sandwich", then you would have seen this note in the SAS log:
Excel XML does not support output from Proc:Gplot
Output will not be created.