Why stopping serving french IPs though? Remove your legal presence in France, sure. But block IP ranges from reaching your servers.. just why?

French law does not care if the servers are in France or anywhere else - just that the users are in France. This sounds unexpected, but that is the law. There is a treaty called the "Lugano Convention" that allows civil lawsuits to be extended across borders of the member nations in events like this - France and Switzerland (where Quad9 is based) are signatories on that convention, so effectively French law can apply in Switzerland on matters involving internet activity. It is much more nuanced than that, so forgive this short summary, but removing servers from France is not sufficient.

Most likely, so they have legal standing to say "We don't operate in your country or serve your citizens, your laws do not apply". Also, punishment for a stupid ruling.