To understand it, and how and why it evolves over time, just like any other study. There’s no such thing as prescriptivist physics, or math, or biology, or etc etc. We don’t get to tell the world how it works, and pretty much no science is focused on that assumption other than historical linguistics.
we could all just speak however we want as long as we understood
We do speak however we want, and we do understand, because we pick up new trends in language on an unconscious level and this is the way languages have always worked and evolved.
then we end up with an uncountable number of dialects and creoles
We’ve already ended up there, and that’s nothing new. Sure, new languages/dialects/creoles creep into the world, but that’s how all languages evolve — instead, the lines between “what’s a language”, “what’s a dialect”, and “what’s a creole” get grayed and more blurry and fuzzy.
The thing is, humans developed language a very very long time ago, and those languages evolve and split off due to large-scale trends in the lives of humans speaking those languages, for a multitude of reasons that interact and make the process essentially random.
Here’s one way to look at it: it’s the opposite of the “jurassic park” problem, instead of “your scientists were preoccupied with whether or not they could, they never stopped to ask whether they should”, linguists spent so much time arguing over prescriptivist/descriptivist arguments, and never asked whether prescriptivism actually can control the evolution of a language.
Anybody, even some random teen in some random neighborhood in any english speaking country, can come up with a new word, and it can catch on and eventually become a new accepted and widely-used word. That’s because it’s a “you can use this if you want” situation, whereas the prescriptivist version is “if you use ___ you are wrong, if you want to be right use ___ only”.
It should be obvious why telling someone they can do something is an easier argument than that they can’t, and this is why prescriptivism has failed. especially because, again, nobody saw “should of” in this post and thought “oh god i don’t know what this is supposed to mean”; instead people either understood and said nothing, or they understood but jumped in to tell people they’re wrong for making them understand in a way that contradicts what their own english teachers in school said they SHOULD be able to understand.