Some of the games are newly added, while others were created a while ago. I've developed all these games myself over the past few years and update them whenever I come across bugs. Typically, when I create new games, I release them as part of a new bundle. For example, once I have 80 games, I'll publish an 80-game bundle (though I'm nowhere near that yet).
Regarding ads, Unity Ads are not implemented in any of these games. Instead, some of the games include AdMob ads, but not all.