After searching for the answer for this, I have found out that there is no crystal Report Version that is able to export a line or box in Excel, therefore gridlines is not appearing,
WORKAROUND: use the field border by formating it manually
However, having this an important function in any reporting tools, we can suggest this to SAP for it to be considered in their updates on their future releases of the product
JUST GO TO THIS PAGE AND HAVE A VOTE UP FOR THE IDEA.
https://ideas.sap.com/SAPCrystalReports/D27006#comments (5 VOTES CURRENTLY)
and
https://ideas.sap.com/ct/ct_a_view_idea.bix?c=A5E8DEA8-D886-4250-BA2B-039F7D32FFC0&idea_id=776FEC64-B932-4159-8C31-759613225B0C (9 votes)
THEY NEED TO HAVE AT LEAST 20 VOTES