Here's why:
* Declarative sentences make statements.
* Demonstrative pronouns (this, that, these, those) point to specific things or people, providing information.
Examples:
* "This is my favorite book." (Declarative sentence, "this" points to a specific book)
* "Those are the shoes I want." (Declarative sentence, "those" points to specific shoes)
While they can appear in other sentence types, they are most commonly found in declarative sentences because their purpose is to identify and provide information.