Take quick scenario evaluation. In Excel, I change one or two cells and see everything update immediately; in R, you need to re-run your analysis and find the outputs you're after again. There is built-in support for scenarios in Excel. In R you have to code your analysis around it, and do the formatting for comparing, too.
Or take the libraries. Anything that is not statistics is just a pain in R. Everything is possible, sure - but high friction. PMT()/IPMT() functions in R? Good luck. Sure it's easy to code yourself (which is the advice you get when asking R users %| ) but I'm using something high level to not have to bother with that sort of thing!
Graphs? Yeah, there's plot() which is straight out of 1960, or ggplot - which is easy for the simple things and then devolves into afternoons chasing obscure manual pages for this or that setting. Here's one: plot 360 degrees of a sine wave, and it's first and second derivatives. Then explain an Excel user how that works. (this is both because anything non-stats is bolted onto R, and because ggplot is designed around stats graphing.)
Keeping a matrix of data, like a simple database? Sure R can read dozens of file formats from CSV to HDF, but actually editing/maintaining that data is a pain in the ass. Excel, just add a sheet and use vlookup - it will let you sort and filter and copy and validate, all without leaving one software package.
Yes, there are many things wrong with Excel. FFS, there is a conference on how to not screw things up in real life with Excel. But saying 'just use R' is silly. For most applications where starry-eyed grad students advocate R over Excel (because hey, nail/hammer, right?), Excel is just the better choice, even if that means workflows that make programming-literate folk die a little inside every time we have to work with them.