Loading .csv files is very slow

Hi,

I found this thing very strange.

When I initiate my experiment, it will load many .csv and .m4a files.
Each .csv file is 7 kB, and each .m4a file is 128 kB.

However, I found that loading a .csv file is much much slower than loading a .m4a.
(I played around with it by removing files from the resource folder)

Any explanations for this? This seems counterintuitive.
Or loading .xlsx file would be much faster?