I am constantly surprised that members are confused about the fact that many native speakers write 'incorrect' English at times. I would hazard a guess that over 90% of English sentences spoken in everyday conversation (if you are lucky enough to be able to identify 'sentences' in everyday conversation) contain things that a purist would identify as a 'mistake'. I should not be surprised if over 80% of English sentences written every day contained 'mistakes'.
The language that is taught to learners is an artificial ideal. Back in the 'good old days' when 'proper' English was still taught, I spent some thirteen years at school being taught what was expected in that ideal. I just about managed to satisfy my teachers and examiners, but many of my colleagues (who were supposedly in the top 20-25% of the population academically) did not manage that.
It makes sense for a non-native speaker to use the ideal as a model, but don't be surprised if you find many native speakers breaking the 'rules' in every utterance they make.
It is true that formal grammar as such has not been taught in many English schools for half a century or so, but that has made only a marginal difference overall, in my opinion. In my adult literacy work back in the 1980s I met many people who were functionally illiterate - and they were at school at the same time as my parents, who used to complain, "In our day everybody left school able to write good English".
I know little of importance about other languages except French and German. Despite the fact that France and Germany have bodies which can decree what is acceptable language in public examinations, I have met in my life many native speakers of French and German who regularly make 'mistakes' in both speech and writing. 'Good' French and German, like 'good' English, are ideals that only a minority of native speakers produce consistently. I suspect that the same is true of most languages.