The answer to this question is rather simple — One cannot be the founder of something that existed before they were born! We believe the scriptures prove that Jesus Christ established His church in the first century, commonly recognized as about 33 AD. Certainly it is true that Alexander Campbell believed in returning to the original standard and practice of Christianity the same way it was practiced in the New Testament without addition, subtraction, or modification.
But when one restores something which has existed earlier, he does not create or originate; he simply attempts to reproduce an earlier work. Campbell and others were seeking to restore the first century church — the one shown established in the second chapter of the book of Acts — which was the one Jesus promised to build in Matthew 16. Therefore, the church of Christ did not originate with Alexander Campbell.