In this specific case is you would rather download 50 to 60go to play each update? suit yourself xDI never understood games that have to be split into parts. It kind of defeats the idea of playing "a" game. Then you play a "games" instead.
more seriously, to some, like me, it would not be a problem because I would be able to download the hole thing in an hour but for some, that can be quite rough. The size means that the download time could be measured in days! for some, that's why it gets split and let's not forget bugs. The longer the game is the harder it become to iron out bugs. so to shorten my answer, it is purely for convenience ( I guess )