테스트 데이터 초기화시 @Transactional 문제 발생 원인에 대해 알고 싶습니다.

package com.project.springproject;

import com.project.springproject.dto.MemberDto;
import com.project.springproject.repository.MemberRepository;
import lombok.RequiredArgsConstructor;
import org.springframework.stereotype.Component;
import org.springframework.transaction.annotation.Transactional;

import javax.annotation.PostConstruct;

@Component
@RequiredArgsConstructor
public class TestDataInit {

    private final InitService initService;

    @PostConstruct
    public void init() {
        initService.initMember();
    }

    @Component
    @Transactional
    @RequiredArgsConstructor
    static class InitService {

        private final MemberRepository memberRepository;

        public void initMember() {
            MemberDto memberDto = new MemberDto();
            memberDto.setLoginId("test");
            memberDto.setPassword("1234");
            memberDto.setName("테스터");
            memberDto.setAddress("서울");

            memberRepository.save(memberDto.toEntity());
        }
    }
}

package com.project.springproject.repository;

import com.project.springproject.domain.Member;
import org.springframework.stereotype.Repository;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import java.util.List;

@Repository
public class MemberRepository {

    @PersistenceContext
    private EntityManager em;

    public void save(Member member){
        em.persist(member);
    }

    public Member findById(Long id){
        return em.find(Member.class, id);
    }

    public List<Member> findAll(){
        return em.createQuery("select m from Member m", Member.class)
                .getResultList();
    }

    public List<Member> findByLoginId(String loginId){
        return em.createQuery("select m from Member m where m.loginId = :loginId", Member.class)
                .setParameter("loginId", loginId)
                .getResultList();
    }

}

위 코드에서 initMember()를 public으로 실행 시 문제가 되지 않는데 private로 설정 시  다음과 같은 오류가 발생합니다.

이에 대한 오류가 왜 발생하는지 이해가 되지 않아 질문 올립니다.