Lichess makes fantastic use of the screen space available, works excellently on all manners of devices, has a native darkmode, and puts the most relevant content front-and-center instead of designing around revenue generation first and functionality second.

Just because damn-near every other website on the internet is comprised entirely of gradients and parallax scrolling doesn't mean any that doesn't is "ugly".

I don't think it is fair to claim that "Lichess is straight up ugly and the interface is just messy" in such absolute terms. While this might be your opinion, I for one like their design a lot and think it's very clean!! (and prefer it to alternative chess websites)...

You making interesting point, with for profit model you can provide better service then with non-profit model to some degree, but it is not always true. There many reasons for such cases, but I think it all comes down to leadership and values of the company, over time leadership and consequently values will change, undoubtedly. Such changes result in higher or lower preference of service to end users versus profits (or innovation, control priorities), I think this is irrespective of for/non-profit organizations.

There are also open source browser extensions for restyling lichess: https://prettierlichess.github.io/

You couldn't be more wrong.

Newspaper websites are full of advertisement and probably the worst sites in terms of UX in the internet. Even if you hide the ads, there's still the constant clickbait and autoplaying videos. Same for paid-by-ad blogs that just use default themes (with notable exceptions like Daring Fireball). Same for any file hosts that doesn't have a freemium model (compare, for example, Mediafire vs Dropbox).

On the other hand, services that offer recurring signatures mostly often have better UX.