> So I personally just don't see the benefit from a less generalised version of coreutil tools

Others have pointed out specific examples, but the general reason (which I don't think I've seen explicitly articulated) is that CSV isn't strictly line oriented -- for intsance, records can span multiple "physical" lines, because line breaks within quoted strings are part of the field value, not separate records -- so line-oriented tools don't work with CSV generally (they may if you happen to have CSV where nothing inconsistent with a line-oriented view happens to be done, but that's luck not something that is generally true of CSV.)