She's doing it to reduce the amount of pics she has to edit with FaceApp. If she wants to post pics without having to edit them she covers her face or shows only part of her face so she just posts them without any editing. Like the recent mirror cellphone pics, everyone knows what her face looks like, there's no need to take pics like that.
I think she initially started doing it because she would always flip between horizontal and vertical on her phone camera in her videos. So she just released the videos as lower resolution 4:3 that flips between the two because she was too lazy to think ahead and pick one camera orientation for the entire video. Since she has that preloaded as her settings in her video editor, she just releases it that way as the majority of her videos. Her subscribers should complain to her and ask her to stop doing it, otherwise she'll continue to do so. I'm sure the majority of people hate it also.