It's just that the web has gotten bigger and more mainstream, and most of us now limit our browsing to a few silos and then act as if everything that no longer bubbles up the filter must have ceased to exist.
But perhaps you are right. Any tips on how to find the new gems?
That's a good question - I don't know. Discovery of anything not SEO optimized is difficult, and a lot of that content was on Geocities and Tripod, so the modern equivalent might just as likely be on Wordpress or a service like Wix, making the design homogeneous even if the content isn't. Ironically, I've found most off the beaten path sites through references in Youtube videos and Reddit. When I was getting my CS degree, the web design class involved building a quick personal site, so URLs connected to colleges might also be a good place to look.
But what's more likely, that no one is writing their own custom HTML sites anymore, or that some people are, but we just can't see them because they exist in their own ecosystems beyond the Googlesphere (and possibly even the Anglosphere?)
...I just realized I'm vaguely arguing for (but not defining the parameters of) a Drake Equation for the web, where N is new personal content. Even if the parameters are low, the scale of the web means N should be significant.
For better or worse, the closest thing today to the feeling of the old personal webpage era is Tumblr. The kids get up to some crazy stuff over there.