You cannot do that with CSV. Simple put CSV is a text based format, that when opened in Excel, is parsed and interpreted by the Excel engine in its own way - another reason why you should not be using Excel for anything! If you have to open output in Excel, then you will need to change your output format to tagsets.excelxp and add in the specific foramts which Excel should apply to each column. You can find examples of this here:
https://support.sas.com/resources/papers/proceedings11/266-2011.pdf
As SASKiwi has already told you, the problem is Excel, not SAS or the CSV file, it is the engine that Excel uses to read the CSV file. If you open the CSV file in anything other than Excel you will see the file is correct (assuming your export code is correct).
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