Do you have an alternative source of revenue to suggest? It might be good to catch the site owner early while it's still small to get your suggestion in.
I mean if they're making direct deals with other businesses instead of just throwing up AdSense I don't really see the problem.
Honestly, a static site that accepted pull requests would cost nothing. Free code hosting on GitHub and page hosting on GitHub Pages or Cloudflare Pages. Literally $0, forever.
It does take time and effort to review pull requests, but there are no $ costs involved.
On the other hand that's a really easy way to handle the community updating the listing. Generate a static page from text files, use PRs to add entries to the text files.
Making advertising very specific, small, essential and not obtrusive, for example restricting ads on each products only to businesses offering services related to that product, I mean not a similar product but that exact one. Imagine searching for a software or library that does X, then on the product/project page there's a small area showing someone/some company offering services (install, customization, maintenance, etc) for the very same product: one per line, no unnecessary graphics or animation, just plain old links, complete with verified customers feedback.
I'm sure, albeit not perfect, this would reassure many potential users, including companies, concerned abut the bus factor or other similar problems that sometime discourage the use of Open Source software.
I mean if they're making direct deals with other businesses instead of just throwing up AdSense I don't really see the problem.