For many years, there was no way of knowing who was on the other end of the phone until you answered it, and you only knew where they were calling from if they told you. It’s not a universal standard that people have Caller ID or that people need to make their information known to it.
I’ve run into this recently with my current freelance client. She works in education and frequently has to call students’ homes from her home, in the evenings. Consequently, she has a blocked (and unlisted) number. Otherwise, any student who disliked the report that she had for their parents could get her number from the caller ID and harass her endlessly.
We also have a blocked (and unlisted) number, as a holdover from my mother’s time in home health care. There was a number for people to reach her but it wasn’t our home number, even though it forwarded to it. That way, when my mother was off the clock the clients who “liked her better” couldn’t call her to badger with questions or beg her to come because they hated the nurse assigned to them that day.
We know people who won’t answer blocked numbers, so we unblock before we call them, it’s an extra three buttons to press, no big deal. If other people won’t answer, so be it. We don’t answer every call we get, either. That’s what voicemail is for.