Interestingly enough, they actually did release a version on DVD with full MPEG-2 video (more info here: https://www.wcnews.com/news/update/13753), but it was an extremely special edition that I think only worked with hardware MPEG-2 decoders. Nowadays, you can play this version with software decoding using some community hacks, but the GOG.com version has the high quality video and has done all the work for you.

EDIT: I was partially wrong. After reading the article, there was a version that was essentially all of the CDs' data on one DVD, but that was replaced with the version I mentioned.