It doesn't, what takes the storage space are all the Samsung additions like their replacement user interface, a load of nonstandard apps and also bundled stuff like Microsoft One Drive, Netflix, Spotify etc.
The same applies to how much RAM is used for cache*. Because all the extras consume RAM, Samsung have enabled memory swap on some of their devices. Try an Android One device and you'll see Android is actually not responsible here for your low RAM and no doubt storage space. *unused apps that are cached will be unloaded to make way for the ones you are using. Android is Linux and it will fill RAM with cached apps to speed up your commonly used apps. Look at www.linuxatemyram.com
