It's also worth noting that the expectations around 64k got higher. We can do so much more in 64k than it was possible in the past. Compression tools have improved. If you take the famous fr-08 intro from Farbrausch and recompress it with modern packers, you would get back many kilobytes. So I think the time investment needed to make a top 64k has increased.

The source code of all my 64k intros has been shared (the last one was added two weeks ago): https://github.com/ctrl-alt-test/demo-archive/ and my plan is to share more code to help people get started. Creating demos using procedural generation is incredibly fun.