Is teaching English (parts of a sentence, etc.) really all that important?

What is the point of trying to force kids to learn what an adverb, or a dangling participle, or a reflexive noun is, when they’re just going to turn around and write an essay in another class that looks like this: “Me and Joe was going to the store. We could of got their earlyer, but there was a car reck and we was hung up.”

Seriously…wouldn’t that time in English class be better spent actually teaching students how to simply write a proper sentence, and SPEAK properly, whether they understand why it’s proper or not? I mean, yes, a teacher who is has a degree in English should be teaching it, so they can explain if a student actually wants to know why something is proper or not (and watch their eyes glaze over in dazed confusion)

I remember in HS having multiple answer questions about which sentence was proper. Without fail, every student could pick the right sentence, but when asked why they thought that was the right one the answer would almost always be, “Because it looks right.” Well, isn’t that good enough?