There's this game called Secret Survey - it's a Unity game, so personally I don't think it has the level of detail that Unreal Engine games have. It's unfortunately abandoned, as no one has heard from the dev in over a year now. Before the dev dropped off the face of the earth for unknown reasons, the latest version of Secret Survey had enough mechanics and sex scenes that it is comparative to Biosshard Arena as of now. And while I don't know how long it took Salt Bake (the developer of Secret Survey) to get to the furthest point in the development of Secret Survey, he managed to do more porn and create a respectable extent of a third person shooter game in a fraction of the time Bioasshard Arena has been in development. Now, I don't know how much harder or easier it is to create a porn game using Unity compared to Unreal Engine, but the gap in progress between the two games is large enough that I'm inclined to think the difficulty in using the two engines isn't the issue here.
Looking through Salt Bake's DLSite page, the first post regarding development of Secret Survey was around Fall 2019. The last post from the author regarding the game was July 22, 2022.
Secret Survey was mostly complete, at least mechanically, at the time of that final post. That's three years. VersusXStudios has been working on Bioasshard Arena (and just Arena, mind you, not Bioasshard proper) since... I don't know, 2017? 2018? That's nearly seven years, maybe six years if I estimate conservatively, and they haven't even finished the Arena yet. The full game will release by the time all my hair has grown grey and I can't even wipe my own ass anymore.
It's absurd how slowly they work. The part that stings is that there's a good porn TPS in Bioasshard, perhaps one of the best in its genre even, but they keep insisting on working on things barely anyone cares about. It's like hiring a carpenter to build you a cottage, and instead of actually creating a cottage, he insists on perfecting the porch's colour and texture while the building itself has nothing to it but the foundation.
If this game had zero promise, I'm sure people like me wouldn't bother peeking into the development of it every half a year or so. What it could be is good, maybe even great, but the longer it takes, the more frustrating it becomes to wait.