Earlier quoted context omitted.
My mother tongue isn’t English and I indeed mixed up rennet and casein because they sound completely different in my language. Natural rennet cheese may be “artisanal” in your corner of the world, it’s 99% of cheese where I live —just in case, 99% might not be totally accurate, it’s an exaggeration to mean “the vast majority”
My mother tongue isn't English either and I live in a corner of the world that has many traditional cheesemakers and a proud cheesemaking culture that goes back centuries if not millenia. Most cheese where I live as in the rest of the world is made with microbial rennet simply because it's cheaper, more available and easier to store and handle. I'm sorry but I don't believe that 99% (or "the vast majority") of cheese…
https://fr.m.wikipedia.org/wiki/Empr%C3%A9surage
“ En France, l'utilisation de présure d'origine animale est une des conditions des cahiers des charges pour prétendre aux dénominations de protections fromage fermier, appellation d'origine contrôlée et la marque de l'Union européenne, Label rouge.”
Loosely translated, it means that for a French to cheese to have one of the protected names (Roquefort, Brie de Meaux, Camembert de Normandie, etc) they must use animal rennet. Since farms making these want the protected names because they sell so much better, they use animal rennet.
In the supermarket you can also buy industrial cheese which doesn’t have to use animal rennet. But at the fromagerie they mostly (only?) sell artisanal cheeses, all using animal rennet.