Why would a company put black lines around the picture in their DVD? I bought a series of children's educational DVD's and they all have these black lines on all four sides of the picture, throughout the whole video.



This is the first time I've ever seen this. Why would anyone do this? Is there any benefit?

I'm trying to understand the motivation of the DVD's creator for doing this.

FWIW, the DVD's are aimed at a market where a significant part of the consumer base will view them on old/small TV's. Maybe something like TV's that were widely used in the West in the 80's.
Old/small TVs tended to overscan their images.  The "title-safe" area was about 90% of the original image.  The DVD's format ensures that despite such overscanning, everything in the image is visible, including the titling shown in red at the bottom of the image, which is hard up against the limit of the frame and thus requires that the image be reduced so that a 10% overscan does not clip it off.