Why does DayZ have so little memory?

The basic game, which you can download on the Playstation, for example, has only a few GB. Games with a map as large as Dayz usually have 50+ GB of storage space, so I assume that the map will be loaded somehow on the server side (or something similar?)? You often notice that when you turn around quickly, you have to reload a lot behind you. But why is it like that? What is the advantage of constantly "reloading" them online? Doesn't that make it massive? For my part, Dayz is also the only game I know that runs so "weird".

Because many textures are used several times in the Map by Dayz, this is also the reason why PUBG is so small

Reloading comes from this because the game is poorly optimized and needs a lot of CPU power, which means that it reloads on weak systems

Thank you