Do people actually like all of the overdesigned clutter to the point where it makes them not want to switch sites?
To me, the stripped down clarity on Lemmy is a feature. I remember back in the day when people flocked to Facebook from MySpace, in large part because they were sick of eye gouging customized pages and just wanted a simple, consistent interface. The content, not the buttons to click on it are the draw right?
In theory, custom CSS is a neat idea, but it’s typically a one-and-done project that is difficult to update, and in most cases, an inadvertent “fuck you” to users who rely on the built-in accessibility of native elements.
Also, custom CSS by users is effectively them placing a code freeze on the frontend.
If a better way of doing things comes along (which is a given in the tech world), you either improve the core site CSS and break the customizations (and hear all about it from your users); improve both (which is a ton of work with no tangible difference in what’s rendered to the page), but now the people who made those customizations need to up their CSS game (which rarely happens); or you do nothing and let entropy run its course and do a total rewrite some day. The last one is literally what happened with new Reddit.