But someone who can't write proper sentences in English won't write anything interesting because 1) the sentence structure will be broken, and 2) they won't have vocabulary sufficient to create an interesting post. I have seen this hundreds, nay thousands(!) of times. And in addition, they're usually too lazy to put any effort into what they're doing. I agree with your sentiment, but I think it'll take some time before the shitposters get discouraged and give up. But I'm patient.
They simply could post in one of the local topics. This forum covers all the major languages. I write in English section with Grammarly extension turned on, which doesn't make my English good of course. But at least it can find some annoying typos and spelling errors. I see your point and think that laziness is the main reason here.