I have never seen a game where there were so many huge files that you have to download for a patch. It looks like to go from 1.3 to 1.4 you must practically download the entire game again instead of just one file to patch the game. Why??

It's often the case on GOG when there are too many changes. Their system seems to be different than Steam, where they seem able to make a diff and send smaller patches (I believe in this case it was 2.9 GB instead of 26 or so).

I think it's something on GOG's side and not the publisher's, but I may be wrong.