because it shows that they don't understand important design aspects
while it doesn't really show off their technical skills because it could be some plugin or copy pasted code, only someone who looks at the code would know better. But if someone care enough about you to look at your code you don't need to show of that skill on you normal web-site and can have some separate tech demo.
Living by that motto is hugely self-destructive.
Creative expression allows us to push ourselves, both in what we think we can do, and often the technical aspects about how we do it too. Even if the idea doesn't stick, you've tried something new.
In a world of Tailwinds and Bootstraps and the same five templates copied again and again and again, let's celebrate the people willing to push things and learn from their inevitable but ultimately valuable mistakes. And let's have some fun along the way.
Why would a frontend developer demonstrate their ability to do frontend programming on their personal, not altogether super-serious blog? I meant that rhetorically but it's a flex. I agree, not the best design in the world if you're catering for particular needs, but simple and fun enough. You should check out dark mode.
In that vein, I think it's okay if we let people have fun. That might not work for everyone, but why should we let perfect be the worst enemy of fun?