Why do so many games have to be downloaded

It is hard to run really large games just from the "cloud"... it slows them down because there is a lot of loading stuff into memory, and the computers that we use only have a certain amount of memory that they can use before they have to start keeping some of it locally (which means we would have to download something). So, only smaller games can be completely online and still be usable. Even online games like MMORPGs (Massively Multiplayer Online Role-Playing Games) require large downloads, even though the action takes place online... because computers can't be fast enough to play the game without storing some of it locally. Computers can access stuff on their hards drives a LOT faster than they can access things online.