Sure, and they sometimes do that if they have to ingest CSVs whose origin they don't control (although not every system implementor cares enough to do it).

But that's still just a bunch of shitty faillible heuristics which would not be necessary if the format was not so horrible.

cat input1.csv input2.csv > output.csv

resulting in a single file containing multiple formats.

Also, what variant is this:

    1,5,Here is a string "" that does stuff,2021-1-1

Is this a CSV file without quoting? Then it's

    Here is a string "" that does stuff

    Here is a string " that does stuff

You can decide to just assume RFC compliant CSVs in the event of ambiguity, but then you absolutely will get bugs from users with non-RFC compliant CSV files.

So, yeah. Can't really be done without making too many assumptions that will break later.

Yes. And my software does that. But it is always going to be a guess which the user needs to be able to override.