Let me try to explain. There’s a murder next door to you. The police suspect you are the perp. The police are interviewing witnesses. The DA is interviewing witnesses. Can you barge into the interview room and demand to be privy to it because of due process? Hell no. The DA builds its case as best it can. Then the DA brings it to the grand jury to get an indictment. Once you are indicted and tried, then you can cross examine the witness.
Let me know if you understand. If not, I’ll try to explain it in even more elementary fashion. I know it’s hard — complicated topic, in addition to trump stuffing your head with ignorant drivel 24/7. But, do try!