Speed limits are a not a good analogy to language rules, partly because they are generally intentionally designed rather than a product of an evolutionary pattern, partly because there is a clear and accepted authority that sets and enforces them with actual penalty, and partly because the consequences for not having them are often deadly.
By contrast, there is no clear authority that “owns” a language and can enforce it’s rules. Some government or academic body might in some cases declare that it has that authority, but they don’t really have any ability to set more than guidelines for how people working for them or producing documents on their behalf must write. Unlike speed limits, which simply would stop existing in a meaningful sense if governments stopped existing, languages existed before any such “authorities” did and would continue to exist if those organizations ceased. As such, I’d argue that linguistic rules aren’t really rules at all in the normal sense, there’s no-one with actual accepted authority to create, repeal, impose or enforce them, they’re just guidelines, loose ones at that, that one should follow if one’s intent is to be understood by someone else using the same or sufficiently similar guidelines. If you understand what someone is saying, which in cases like “should of”, people calling it against the rules clearly do, then they have succeeded in that goal, so it cannot really be a failure at being literate.
I reject any notion that this will eventually overcomplicate language to the point of it being too difficult to learn or use, because ultimately, people are not born knowing it, they must all learn, so any language too complex to learn wont be learned and therefore won’t be used, and similarly, any language too complicated and unclear to be used to communicate, can’t be used, and so won’t be. The complexity of language is inherently self-limiting at a level that prevents it from becoming useless.
Or for a TLDR: we don’t have to change the rules to accommodate people breaking them, because there aren’t really any rules at all.