Firstly because it makes me laugh, but also it's because it's actually gatekeeping other people's language that is excluding and antisocial. I firmly believe that we ought to accept the language that others use when the speakers intention is clear, even if they "don't speak good". The uneducated don't deserve scorn by default just because nobody rapped them across the knuckles when they used "coz" instead of "because". And that's ignoring even that many of these grammatically incorrect but often used phrases come from minority groups and shitting on people for using them is actually a subtle avenue for (probably unintended) racism.