If instead you surprise them with it in an interview, they can't do it, and you don't hire them because of it, well, they are the ones that dodged a bullet not you.
I know about third normal form because I learned it from my girlfriends open-on-the-ground textbook in college. It's just not that hard.
Same goes for Leetcode. Anyone can Google how to implement some algorithm, but you won't be told what algorithm to use in your project requirements.
Of course, an interview could just involve getting you to give general descriptions of things instead of implementing them, which would satisfy this to some degree. But then everyone with a bachelors would pass the interviews, so they had to make them more intensive in order to limit the pool further.
Likewise there are plenty of people who have learned database design through a combination of optimizing execution plans and dealing with the practicalities of schema changes. Such people may never have heard the term "Third Normal Form", but will run absolute rings around a college newbie who has. Indeed, in my career I have met at least two people responsible for database design who did know normal forms but did not know about execution plans, or covering indexes for that matter. Or had a nice normal set of tables, and then proceeded to build a reservation system (hit by 100,000+ users when registration opens) that takes a transactional lock on a single row using an ORM. They understood database theory from 1971, but they didn't know what this specific database implementation actually does.