To give more control to image owners about what displays on their image page.
People have asked to be able to delete comments on their images, but this would allow silencing dissenting opinions and targeted attacks and give an incorrect view of the Imgflip community so we have not added it. Disabling comments affects all commenters equally.
Also, some people share outside the Imgflip community and only want to share the image, not share a comment section which may be unrelated to their reason for sharing.
Artists may also prefer no commentary on their art, which is an option we'd like to give.