Natural primary keys (email, ssns, etc) was the standard for a long time. It was some kind of platonic ideal. Artificial keys were wasted space of random data that didn’t belong in a database.

When I was in college, academics were just starting to grudgingly accept artificial primary keys (like UUID or auto-incrementing integers) as a concession to reality.

To a modern developer natural primary keys sound insane. Artificial keys are faster in almost every way due to index size. You’re storing compact, fixed-size binary data instead of strings.

You see it a lot with Java devs or others who think in OOP objects and then try to simply push those to a table. That said it’s a little more rare now, since most ORMs helpfully auto-creates PKs for you as an int or uuid.