.cbz and .cbr files are actually ZIP and RAR archives. They're not that special. You can open them up with WinRAR, 7-Zip, etc and you'll see a bunch of images inside and these images almost never fit the "standard" 600x800 resolution or aspect ratio from today's e-readers.
ePub is also a ZIP archive except nobody bothers with fullscreen (600x800) images, mainly because when you choose a different font or font size they will be pushed down a little and end up spanning across pages. ePub wasn't designed to be a photo album.
These have very different usages.
Benefits? What kind of benefits? Compression? JPG and PNG images are already compressed, just like MP3, AVI, etc. Let me ask you this, have you ever tried to archive a 700 MB (DVD Rip or otherwise) .avi file? It usually ends up 698 MB or so... That's because it's already compressed. Same with JPG and PNG. If you set the highest compression method you'll only save a few bytes, maybe a couple of kilobytes or so. And the e-reader would have to work extra hard to switch between pages. Not really worth it.