Why is Steam Redownloading the whole game?

It’s a way of updating files by issuing a patch file that goes through the files you have installed and make necessary changes. The alternative is that instead of a small patch file to download, you will be forced to download large amounts of data, possibly the entire game, every time the developer updates the game.

Why is Steam patching the whole game?

Steam only downloads and updates what the game creators tell them to update, so If the game is poorly formatted by the creators, and everything is only contained in one or two files, then steam has to download that one file that changed in its entirety since saving part of a file then combining parts of a file is a …