You know most games on iOS are on rails of some sort, you have to go to or follow directions to a certain spot if you don't make it in time you lose.
Yes they could have made it with more freedom to the player making the game let's say 900Mb or over a Giga in size. I'm sure if more games were equal in graphics & "more playable" they could save all these games in iTunes & load the one they feel like playing.
Even I still have 10Gs left on my iPhone.