It's not that Excel can't support that long of a number in general. When you open up a csv in Excel, it is not being worked on in "Excel format" where it is dis

It's not that Excel can't support that long of a number in general. When you open up a csv in Excel, it is not being worked on in "Excel format" where it is displaying the number in scientific notation but it is still retaining the full number. If you click on the cell in the text window in the top it shows you the full number. The asinine thing happens when you save it back as a csv. Excel doesn't think to itself "hey, I should write these full values I have stored in each cell to the csv file". It just writes whatever is currently displayed to the csv file instead.