Here's why:
* Appositives are noun phrases: They function as a second noun phrase that renames or explains the first noun.
* Verbs express actions or states of being: They are essential for creating sentences, but they don't belong in noun phrases.
Example:
* Incorrect: "My sister, *who loves to bake*, is coming to visit."
* Correct: "My sister, *a talented baker*, is coming to visit."
In the incorrect example, "who loves to bake" contains a verb ("loves") and is a clause, not an appositive phrase. In the correct example, "a talented baker" is a noun phrase and functions as an appositive to "sister."
Remember: Appositives are always noun phrases, and noun phrases cannot contain verbs.