Putting any of those monsters into a movie not specifically designed to see how loud an audience can boo would arguably be the boldest decision in cinematic history.
There's a Terrifying Implied Backstory
OK, so in that first Power Rangers episode, Queen Rita's escape and subsequent attack on Earth provokes tube-faced ethereal commander Zordon to send his effeminate sidekick Alpha 5 to locate "five overbearing and overemotional humans," to which Alpha 5 immediately responds, "Not teenagers! I was afraid of that!"
"Please, Zordon ... I can still hear their screams."
In other words, this isn't the first time he's been told to wrangle teenagers for Zordon. Just how many moody high school students has Zordon burned through in his intergalactic defense league? Hell, Alpha 5's name tells us he is the fifth in a series of robot servants -- we actually see Alpha 4 entombed in a cardboard box and a death shroud of cobwebs:
Pictured: The "Peace Conference" Trini and Zach went to.
There's probably a box full of teenager bones somewhere in Zordon's attic. With any luck, we'll get to see that box in this big-budget reboot, because that's the Power Rangers movie we deserve. And not that Turbo bullshit.