Poetry - Why Must There be Iambs?

Iambics are the sky through which words fly
Formations sweeping all five seasons across
In order royal and in right service to
The aspirations of all noble youths

For verses built without a careful plan
Fall but as clutter on a wasted page
Their meanings and intents broken apart
And lost (like sophomores between each class)

Free verse is only an unanswered why:
Iambics are the sky through which dreams fly