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