Well, I'll answer for both. Some people correct others to show off that they know their Grammar, for others it drives them insane so they correct other people hoping they'll change how they type. As for why people use correct grammar, it's just a preference. I hate reading things multiple times to understand what they said. Hope I helped!(:
In which way, correcting other people or writing complete sentences and punctuation?
Sometimes because bad grammar is just a pet peeve.
The word is grammar! Grammar! Not Grammer!!!
sorry, could not resist