>> Pretty much everyone can solve it, but I’m not just looking for them to solve it. ... Almost no one passes.

Sounds like a not-great process IMO. You're expecting them to understand a lot of what makes you tick and what you personally consider 'maintainable' based on a 1 minute problem description.

My opinions on what makes code maintainable have evolved and fluctuated (based on most irritating current problem) significantly over time.