Hear me out. If you all have noticed, with every privacy feature released a significant amount of people migrate to it full-time. I currently cannot recognize my phone ring, because from the day I bought my last phone I switched off the ringing and never bothered to turn it back on, not because I hate ringtones, I just forgot and also there have been no dire consequences to do so. Someone on this thread also said he/she set her phone permanently on "do not disturb" and just deals with notifications when they want to. This is all well and good cause anyone who has tried to reach us has successfully done so and even if they did not reach us, we have evidence that they attempted to.
Having a whitelist system is VERY different and has many unforeseen consequences. From as little as, your mother got a new phone and soon she cannot reach you, you got a beautiful girls number and want to ask her on a date but cannot reach her. To bigger issues like your teenage child is mad at you and deletes your contact from their phone. Job offers will be missed, you will become unreachable in emergencies etc. The short of this is, the best case of such a feature is that you don't need to install a third party app to block spam calls, the worst case of such a feature is people can literally die cause they cannot contact you or vice versa. If I was a phone manufacturer. I just won't even allow this. There are easier ways to solve the underlying problem without opening the door for worse outcomes