Edit : I do remember the half a dozen I use or might really need, and already feel like an outlier. ( And as pointed in another comment, they're already 11 digits each. Not that much of a difference. )
Children do, or should. Even very young children should be taught until they have memorized their own phone number.
And even older children might not have phone yet, but still need to be able to call home.
Yup, all the ones I knew as a kid in the 80s and early 90s, and haven't used for 2 decades.
I have no problem at all remembering my 22-digit IBAN. I know people who memorize random-generated 30-character passphrases. But yeah, we don't seem to be the norm.
Because that mean re-inventing the phone system and making it incompatible with all existing and future devices made for the whole rest of the world.
These are going to be for 5G IoT devices anyway, the phone number is just going to be for billing use, all the actual traffic is going to be over IP