One thing about not using a prompter is that the media won’t have an opportunity to slam Cruz until after they hear what he says which means more people will get what he says unfiltered. That definitely knots their panties in a wad.
The teleprompter is a control mechanism. It allows the powers behind a persona to script the actor they are backing.
A person without a teleprompter is uncontrollable and therefore extreme, radical and frightening (to liberals).