Short quote: because
Last thing first: the charge of laziness. Commenters on usage quite commonly attribute the motive of "laziness" to the user of any variant they believe to be incorrect/wrong. The idea is that the writer or speaker was too lazy to find out what the correct/right variant is — or if the writer or speaker believes that their variant is in fact correct/right, then they were too lazy to have learned otherwise ("they should have known better"). It's not enough to say that the variant is incorrect/wrong, but the user of the variant must also be maligned.