Websites and apps that feel like quality are generally made by people who can achieve it. You'll get shit static sites or shit SPAs if you have shitty devs. It's not beyond reason. If you are shitty chef, your food is going be shitty. So yeah, here's the big secret about programmers:

They are mostly shitty

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Interestingly, every landing page or website for recent AI apps have looked AMAZING. Designers and standard website developers are totally on point. It's just, crappy developers who can't create a rich experience on top of incredible design that's the issue. CSS is not going to fix what can't be fixed (some people are not supposed to be in this profession, but hey, it pays ... for another three or so years).