Earlier quoted context omitted.
Humans generate decisions / text information at rates of ~bytes per second at most. There is barely enough humans around to generate 21GB/s of information even if all they did was make financial decisions! So 21 GB/s would be solely algos talking to algos... Given all the investment in the algos, surely they don't need to be exchanging CSV around?
CSV is a questionable choice for a dataset that size. It's not very efficient in terms of size (real numbers take more bytes to store as text than as binary), it's not the fastest to parse (due to escaping) and a single delimiter or escape out of place corrupts everything afterwards. That not to mention all the issues around encoding, different delimiters etc.
Depends on the distribution of numbeds in the sataset. It's quite common to have small numbers. For these text is a more efficient representation compared to binary, especially compared to 64-bit or larger binary encodings.