And that's also why we remember it. It's from a time we used to remember phone numbers (smartphones weren't around, in many countries even normal cell phones weren't widespread yet, and even those had limited memory and usually no way to migrate to a new phone (the SIM could store entries too but had laughably low capacity, like 25 entries with max 9 letters for the contact name)).
So, committing them to memory was just a thing. And our brains get less plastic with age. I can remember my home phone number from 1982, but not my last cell number (before the current one) although I used it for 3 years, as recently as 2014. The insane amount of information streaming in front of our senses probably also triggered some unconscious attitude adjustment (not going to bother remembering any of it, if it's important I'll write it down).
So, committing them to memory was just a thing. And our brains get less plastic with age. I can remember my home phone number from 1982, but not my last cell number (before the current one) although I used it for 3 years, as recently as 2014. The insane amount of information streaming in front of our senses probably also triggered some unconscious attitude adjustment (not going to bother remembering any of it, if it's important I'll write it down).