Maybe for the pages you tried, but I see ads on these pages:
https://neal.fun/infinite-craft/ (bottom)
https://neal.fun/perfect-circle/ (right)
https://neal.fun/days-since-incident/ (bottom, near the end, above the "you may also like" section)
The last one occasionally fails to show ads due to some javascript error (visible in the console). The same error was also observed on a few other pages with the "you may also like" footer, so my guess is that some ads were supposed to be visible on many pages, but were accidentally hidden due to some configuration issue.
For comparison, at one point slither.io, which is another browser game (not his project) was bringing in $100k/day from one ad unit showed each time the player dies https://www.wsj.com/articles/as-slither-io-goes-viral-games-...
If the avg player dies 10 times, and the ads shown had $.5 CPM, then to make a dollar you'd need only 200 players. So to make $100k/day you'd need 20M daily actives, which is very high but it was really popular around those days.
Is 20M daily actives possible? Yes, because if the average play session is 15 minutes, with that many players you'd have ~200k concurrent players. There's currently a game on Steam called "banana" where you just click on bananas, and that one has 292k concurrents. There are also several Roblox games with that many concurrents, so it checks out.
... which is part of why everything seems so polished, they each express an idea without compromise, and when he's done he can just be done.
Someone could make a pretty good museum exhibit from his site.