Dead By Daylight patches reinstall the entire game.
I've been wondering for quite some time on why this game would take FOREVER to update despite the patches being only a few hundred megabytes in size. Now I know that the entire game re-installs itself while updating. Why is this like that? I've had no issues with other games because they've never had to do this.

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I can't tell for sure, but I know that Path of Exile and SW:TOR sort the files anew to conter errors and to tidy up the data files. These games also need ages to update even if it is just 500Mb. This could be the same here.