Answer: Because they don't have five feet in the line or don't have an unstressed syllable followed by a stressed one like iambic pentameter requires.
Explanation: In poetry, an Iambic Pentameter is a metrical speech that has 5 feet on every line. A foot is a pair of syllables in which there is an unstressed syllable followed by a stressed one.
The lines "As wicked dew as e'er my mother brushed" and "With raven’s feather from unwholesome fen" follow the rules of iambic pentameter, while the line "Upon thy wicked dam, come forth!" has just four feet, and the line "Drop on you both! A southwest blow on ye" doesn't have the unstressed syllables at first.
Answer:
The line 'So Eden sank to grief' is an allusion, or literary reference, to the Biblical story about The Garden of Eden, a perfect paradise until Eve ate from the Tree of Knowledge. By making this reference, Frost is implying that the idea nothing good can last is an old one; it's part of our human experience.
Does it use the words "like" or "as". The two possible answers are metaphor or simile