I can't answer any questions about the artist specifically, as I've seen their artwork before on DLSite, but never looked into it. I can offer a theory as to why it's difficult to find these games, however. You see, someone has to actually buy the game in question, and then decide to upload it on the internet, allowing others to ignore the moral of paying for things via both doing so through legally questionable means. The people who do this, especially for h-games, are most likely in the far minority. Said people probably don't have endless cash, and don't want to buy games they wouldn't like. Therefore, more popular games are more likely to be pirated and spread, as the odds of someone of those people getting the game and uploading it increases, due to more people playing it. The kind of games that I've seen the artwork from this artist for don't seem to be popular, or at least I've never seen mentions of them outside of DLSite. This means that people aren't willing to talk or don't know about the games, and therefore can't buy and upload it. Therefore, the reason why there's no downloadable versions on alternate websites is because it's not widespread or known enough for people to bother.
TL;DR: The games aren't popular, so the uploaders would rather focus on getting the more well-known games rather than the ones that aren't safe bets. No need to aim for a niche in a niche market when there's many h-games that do better that still need translations and uploads. Hope this helped.