Here's why:
* Conjunctions connect words, phrases, or clauses. They usually indicate a relationship between the elements they connect, such as addition, contrast, or cause and effect. Examples include "and," "but," "or," "because," "so," "although," etc.
* "Not only that" is actually a phrase that functions as an adverbial modifier, emphasizing a point or adding to a previous statement. It's often used to introduce a second point that reinforces the first.
Here's how it's used:
* "I love her smile, not only that, she's also incredibly kind." (The phrase "not only that" emphasizes the second point about kindness.)
To use "not only that" as part of a conjunction, you would need to complete the phrase, for example:
* "Not only that but also..."
In this case, "not only...but also" acts as a correlative conjunction, connecting two parallel elements.