OK here's the problem: the csv is not actually a csv. So, in essence, this is a problem with the file itself. Below I'm describing how I figured this out, though I'm sure there are other ways to deal with this using base R, a text editor, etc.
In Excel it the file as though the file is a csv (I don't know the innards of Excel well-enough to know how this is accomplished), but, when you open the file in a text editor, you can see that there are not actually commas, there are tabs!
It also has some unusual encoding settings, so, when I re-saved it (file, save as) in a text editor, I switched the character encoding to UTF-8.
Below, see with encoding as UTF-8 and proper line endings in CSV file vs TSV.
This might not be a great way to do it, but, this
did allow me to at least see all of the data when I went to preview it in RStudio (you can't open the full file in the text editor because of the size, but I could see it all in
File >> Import.
After switching the character and line-ending encodings in the text editor, I could see all of the rows, but they were prepared to import as a single column (because there were no actual commas). By switching the delimiter from comma to tab, it automatically changes the configuration (albeit using the readr package, as opposed to base read.csv).