Can you say more about that?

Times have changed. While there are significantly more open-source projects, online communities, and all kinds of available help than ever before, the proportion of active contributors relative to the number of people online has decreased. Consequently, the time required for each volunteer to process input for a project like a "webring" has increased significantly.

I also feel that it's become harder to motivate people, but not because they've become lazier. Rather, the tasks have become more demanding, so "nobody seems to have the time for them anymore".

By every measure don't people have more time than ever before? I think it's more a dramatic shift in how people use & view the internet. The (unfortunate in a lot of ways) answer is probably create something new and exclusive, but universal enough for the target audience that's going to do all the work to align incentives, try to pull along the good and leave behind the bad. There has been and will continue to be a lot of false starts & failed attempts. If successful it will eventually be co-opted and ruined too. So it goes.