Big big reason: R doesn't alter data without being asked to, Excel does so, silently, sneakily. Anything important should not be done in Excel. https://www.theverge.com/2020/8/6/21355674/human-genes-renam... https://stackoverflow.com/questions/165042/stop-excel-from-a...
"Floating-point arithmetic may give inaccurate results in Excel" https://docs.microsoft.com/en-us/office/troubleshoot/excel/f... "Align numerical precision Excel 2013 and R" https://stackoverflow.com/questions/39531655/align-numerical... "Numeric precision in Microsoft Excel" https://en.wikipedia.org/wiki/Numeric_precision_in_Microsoft...
IEEE 754 just has unintuitive properties.
Kahan (the "father of IEEE 754") has a rant (among many others) about Excel as well, and how it tries to hide some of the floating point complexities more or less successfully:
Floating-Point Arithmetic Besieged by “Business Decisions”