When did this happen? I remember judges at hackathons used to be very forgiving about lackluster UIs as long as the idea was cool and at least functional by the presentation time

It depends a lot on the hackathon/what the judges are looking for. A few are run by technical people who pick the coolest technical architectures, a few are run by casual users who pick the best looking result.

The majority of the ones I’ve been in have tended to be run by people who judge based on their notion of how useful the app will be societally, with the tie breaking factor being the UI/architectural design.

10+ years ago, when most "grassroots" (and some of the better startup) hackathons were displaced by enterprise-sponsored hackathons. I can mostly talk about the Berlin hackathon scene, but as far as I understand it the same thing happened in SF/London as well around the same time.

Presentation-first judging has been a thing for a long time, and unless there is a organizing party that explicitly makes code reviews a part of the scoring, and the organizers ensure attendance quotas for different personas (engineer vs. product vs. designer) it will always drift that way.

It's more about unconscious bias. The slick smoke and mirror will simply show better.

Reminds me of the inconsistency of take home interview tests where you have no idea if the person reviewing cares that the UI is shiny or not or if they want you to write a novel in the readme and make it look like a real project.