Because they are all names for the same thing; ie one God

Jesus Christ said "I and my Father are one". God the Father, God the Son, and God the Holy Ghost are one God in three Persons. Jesus Christ is JEHOVAH in the flesh. There are various portions of scripture in the King James Bible that support this. Thank you and God bless you!

One of the earliest Apologists was Justin Martyr, who lived from about 110 to 165 C.E.or some 77 years after Jesus death and some 10 years after the death of the last apostle..John. None of his extant writings mention three coequal persons in one God. For example, according to the Catholic Jerusalem Bible, Proverbs 8:22-30 says of the prehuman Jesus: “Yahweh created me when his purpose first unfolded, before the oldest of his works. . . . The deep was not, when I was born . . . Before the hills, I came to birth . . . I was by his [God’s] side, a master craftsman.” Discussing these verses, Justin says in his Dialogue With Trypho: “The Scripture has declared that this Offspring was BEGOTTEN by the Father before all things created; and that that which is begotten is NUMERICALLY DISTINCE from that which begets, any one will admit.” Since the Son was born from God, Justin does use the expression “God” in connection with the Son. He states in his First Apology: “The Father of the universe has a Son; who also, being the first-begotten Word of God, is even God.” The Bible also refers to the Son of God by the title “God.” At Isaiah 9:6 he is called “Mighty God.”...... But in the Bible, angels, humans, false gods, and Satan are also called “gods.” (Angels: Psalm 8:5; compare Hebrews 2:6, 7. Humans: Psalm 82:6. False gods: Exodus 12:12; 1 Corinthians 8:5. Satan: 2 Corinthians 4:4.) In the Hebrew Scriptures, the word for “God,” ’El, simply means “Mighty One” or “Strong One.” The equivalent in the Greek Scriptures is the‧os′. Moreover, the Hebrew term used at Isaiah 9:6 shows a definite distinction between the Son and God. There the Son is called “Mighty God,” ’El Gib‧bohr′, not “Almighty God.” That term in Hebrew is ’El Shad‧dai′ and applies uniquely to Jehovah God. Note, however, that while Justin calls the Son “God,” he never says that the Son is one of three equal persons, each of whom is God but the three forming only one God. Instead, he says in his Dialogue With Trypho: “There is . . . another God and Lord [the prehuman Jesus] subject to the Maker of all things [Almighty God]; who [the Son] is also called an Angel, because He [the Son] announces to men whatsoever the Maker of all things—above whom there is no other God—wishes to announce to them. . . . “[The Son] is distinct from Him who made all things,—numerically, I mean, not [distinct] in will.” The New Catholic Encyclopedia states: “The formulation ‘one God in three Persons’ was not solidly established, certainly not fully assimilated into Christian life and its profession of faith, prior to the end of the FOURTH CENTURY. But it is precisely this formulation that has first claim to the title the Trinitarian dogma. AMONG THE APOSTOLIC FATHERS, there had been nothing even remotely approaching such a mentality or perspective.”—(1967), Vol. XIV, p. 299