When you press and hold the spacebar on your desktop or laptop, it causes a space to be continually inputted until you release the spacebar. On iOS' virtual keyboard, it doesn't work quite that way. Instead of continually inputting a space, tapping and holding the spacebar inputs a single space and then stops. If you want to put in a series of consecutive spaces, you must continually tap the spacebar key on your virtual keyboard.
Space+ is a new jailbreak tweak that allows you to adapt desktop spacebar key functionality. Take a look at our full video walkthrough inside.