Here's why:
* It describes an action: "Beckoning" means to signal or invite someone to come closer.
* It can be used as a present participle: You can use "beckoning" as a verb in the present participle form, like "The lighthouse was beckoning the ship."
While you can't use "beckoning" as an adverb or adjective, you can use words derived from it:
* Adverb: You could use the word "beckoningly" as an adverb to describe how something is beckoning, for example, "The cat sat beckoningly by the door."
* Adjective: "Beckoning" can be used as a participle adjective to describe a person or thing that is inviting, for example, "The beckoning lights of the city."
Let me know if you have any other word questions!