This is a wider range issue with the recent artistic revolution going on in Japanese art right now. Before, most studios employed art styles that were complex and diverse, nowadays, they use highly simplistic art which success ultimately inspires H-artists which is where we are now.
I guarantee that if this game was released in the 90s or early 2000s, and that technology was a bit more advanced back then, we'd be seeing way more games like Solo Leeching. The artists of back then are simply a different breed when compared to most artists today.
I dunno about this. There's a sheer volume differential when you're talking about h-games/hentai/anime from the 90's/00's to now. Not to mention a clustering effect where we pretty much get everything translated and brought over as opposed to what specific translators choose (even more evident in the porn space as that was even more affected than non-hentai/etc). Aside from the one and done artists, a lot of studios from back then that are still producing are still just plugging away with their art now. i.e. 2990, beelzebub, empress, etc.
If anything I feel like just with the quantity of new works, the variety has been on a big uptick. Since it's less about what percent of games come out like that and more about just the flat numbers we see. Not to mention western devs starting to toss their hat into the fray (crowd funding, steam allowing AO games, etc).
Sure there's gonna be popular depictions, but that's true for any time period (lots of spider plant hair girls in the 90's/00's). But realistically... vanilla porn involving young women with giant bazoongas, hourglass figures, and affable/flat personalities will probably always sell better than any other type.
