This can’t be all of them. My business partner and I delisted our tiny (unsuccessful) indie game after we wound up our company and our game doesn’t show up here.
Ultimately, all the datasets on Steam are scraped one way or another, since Steam themselves don't seem to publish it. I could be that they simply never came across your project before you delisted it, and of course after delisiting it I don't think they'll ever come across it.
Hm yeah. We removed it a few years ago now so I assume they should have found it though. We followed these instructions and had to contact valve and give a justification https://partner.steamgames.com/doc/store/retire_app I don’t remember the details of the form but maybe there were options and one amounts to being delisted and another amounts to just no longer being visible and available for sale.
"Deslisted" == "no longer being visible". If it's delisted it won't show up in search results, tag listings and more. So if you just had it online for a few weeks, that was the only moment the scrapers could find it. If they didn't catch it at that point, they'll never catch it.
The nice move in this scenario would have been to make the game free instead of delisting. Gamers can still enjoy it, and you don't have to worry about income once the company is closed.
It actually is free on itch.io, and people on steam who bought it still have access to it. Keeping it on steam required us to maintain our company registration which we didn’t want to do since it’s a waste of money and time as we weren’t planning on doing anything more with it.