BMW's being kinda quiet about why the i5 doesn't have a frunk, but the rumor is that not enough people actually use them, so they don't think it's worth the effort. They're using the extra space under the hood for electronics and stuff, which takes up frunk room. A BMW designer also pointed out that even without a traditional engine, electric vehicles still have a motor, and the battery and its related systems require space, which can limit the room available for a front trunk.