The "gambling" games, in the way you're describing, are just reskins of classic games with hentai art and visuals. They're no different from light puzzlers (i.e., connect-3, jigsaw) to be rewarded with a piece of art and are generally terribly boring. Typically, I feel that they are either a gateway to get one hooked on something else or are simply a cashgrab. Most players, I feel, will ignore most of these with a slight but noticeable exception with the connect-3 style of games. (Of course, I'm only looking at the digital angle here, and not just pack of real world cards with lewd art -- 'cause a pack of cards aren't games by themselves.)
(Answer) Unique card systems are much better suited for hentai, more profitable, and are more rewarding for the participants even if it's a gimmick. There is a vast swath of games that already exists in the real world in both physical card stock and digital styled tabletop games. These games also run the gamut of simple to confusingly complex. Many are based on the living card model and others can be full RPGs using cards (with varying degrees on how explicit they can be). (Less explicit physical items simply sells better in the real world.) In addition, the push-your-luck mechanic can also be found in many of these different systems / games and aren't simply regulated to those "gambling" games mentioned in the OP.
The living card model is often seen with just the base and possibly an expansion since the games tend to be smaller, niche publications that cannot target the wider mainstream audience due to the adult content matter; and complex RPGs-esque games are even more limited. In the digital realm, this is much, much easier to pull off and there are many, many more games that are found. That's because it's cheaper to do than physical counterparts and provides more sale opportunities. For instance, the logistics of just finding partners to produce, store, transport, and sell will eat into any kind of profits (if the game sells at all); hence, they tend to be more expensive than other, better games found amongst the others in a store that would carry them. Whereas, a lot of this overhead is removed from the equation when it comes to digital formats especially in the mobile market. **They're more accessible, easier to maintain and produce, and have numerous ways of generating income for the game's holders.** In regards to the latter, there are many ways how that's done such as incorporating a gacha mechanic or paying for mini-DLCs for additional content. It's easy to see why there's an explosion of content on the digital front, and why unique systems are better suited for hentai games than simple gambling games as the way it's described here.
Hope that helps. As always, stay safe out there!
