screamingmetal
Super Freak
They didn't have a cloaking device yet.
The Federation doesn't use cloaking technology (at least until the Dominion War). Roddenberry said the reason is that "the Federation doesn't sneak around". But it would prove to be so incredibly useful in space exploration like following the Prime Directive, that it doesn't make sense not to use it.
The simple reason I believe it's not used is because people want to see the spaceship zooming around.
Even in old Trek there's head scratching things done just for the effect.