it is impossible to track my iPhone if they turn it off

If your iPhone is stolen, and they remove the SIM, you can't track it

If your iPhone is stolen, and they wrap it with aluminum foil, you can't track it

If your iPhone is stolen, and they put it in a Faraday pouch, you can't track it

If your iPhone is stolen, and they drop it in a shoplifter’s shielded shopping bag, you can't track it

If your iPhone is stolen, and the battery runs down, you can't track it

Being able to turn it off is irrelevant if your phone is stolen; you aren’t going to get it back. Suppose you could track it. Would you confront the thief? People have been murdered doing something that foolish.

And requiring a password to turn it off would be a huge inconvenience to everyone whose phone has not been stolen, not to mention making it impossible to restore it if it is disabled, because the first step is to turn it off.

BTW, you aren’t original; this has been discussed over and over for 10 years.