I have a lot of problems with style guides. The first is that grammar is not rigid or inflexible. Grammar has been in a constant state of change since its very inception. Every single generation has changed the grammar of its language, and no matter how hard the generation in power struggled to stop their language from changing, it has. Not even the printing press or the myriad style guides that have been written through the ages have kept language from evolving. The idea that language should be caged destroys the very fundamental purpose of language.
Language is about communication and expression. The ultimate reality, and really the only rule of language is that the words I say need to make you understand the things that I’m thinking. If you understand me, then my language is correct. The only grammar that matters is the grammar that aids in the understanding of language. Keep in mind here that I know a LOT of grammar. I soaked that stuff in like a sponge when I was young and I haven’t forgotten it. I know and enjoy a lot of the standard conventions of English grammar. For example, I think that Oxford commas are absolutely critical and the idea that they are optional is shameful and wrong; they are often essential to aid in communication. However, some conventional grammar rules are stupid as hell. Not ending sentences with prepositions is moronic bullshit. The same for not being allowed to use “hopefully” to mean “with hope”. When everybody knows what I mean, then my language is correct.
Beyond that, though, language is too complex to fit in a book. If you tried to create a rule for every single solitary possible event that could arise in English, your guide would be so unwieldy as to be useless. And if you did know how to navigate the guide and managed to learn all of those rules, you would be the only one that knows them. And once again, who cares about imaginary rules that only you follow? If it isolates you from the rest of language speakers, then it hinders communication.
Ultimately, though, what bothers me most about style guides is that they are STYLE guides. They aren’t telling you that something is right or wrong; they’re telling you how to write specifically in a certain way. Once again, I find these to often be a hindrance to communication. (Hey look, I just noticed that I split an infinitive. It did not in any way whatsoever impede my ability to communicate.)