Because developing an adult 3D game is a WHOLE DIFFERENT LEVEL of time and investment than any other game, especially the games posted on this site which are 90% RenPy/RPGM.
The vast majority of 3D games here are rip-offs which all reuse the same assets, low-poly models, have clipping and 0 attention to detail. TML has their own model, animation, rendering, paid voice actor, decent optimization, etc. In fact, I'd say the current approach of TML is probably
the most unproductive way to earn money, by the time it takes to complete games like this, those who have the skills to makeit ended up finding a real job which pays 2x higher.
No need to look at the past, actually. Look at the recent adult 3d games on DLsite/Steam and tell me, is this the type of games you're looking for and the industry you want to support:
- rushed games which all reuse the same 3d assets, low-polygon models, lazy sounds and story
- with tons of bugs, clipping in animations, absurd difficulty or level design, because the developer did not have time to test the game
- who don't care AT ALL about the non-Japanese market because it is not profitable enough (so we get shitty MTL translation/censoring)
These are sometimes good games, don't get me wrong, but it's clear that the devs do not have time to do what they wanted. That's what you get when you want to keep the costs as low as possible and squeeze the dev to work as fast as they can.
Keep in mind, someone who makes a good game which gets 5 000 sales on DLsite (and say 10$ per sale), that makes him 50 000$ before expenses, DLsite margin, and taxes, so something like ~25 000$ income after. That is 2x below the average annual salary of a normal developer so you have to pump literally 2 games per year just to get a normal salary, and you still don't have all the advantages of a normal developer (eg. building a career, knowing that you won't get unemployed in the near future, and that even if you do your experience will be useful for another job).
The adult game industry is extremely niche, especially outside of Japan. You cannot buy a game 10$ and expect the dev to live comfortably with it. The "thousands of indie games" you're speaking about are targeting a casual audience which has MILLIONS of potential customers, so they can sometimes make profit out of it, but DLsite top sellers rarely exceed 10 000 sales.
Have you ever wondered why we see more and more fiascos like Cyberpunk, Fallout 76, BF2042 ?
That's actually for the same reason.
Basically, the video game industry only attracts bad developers nowadays, because good developers, have realized that the video game industry is too stressful, too poorly paid, and too risky in general.
15-20 years ago, developers were viewed as nerds, not really considered a real job, so good developers were OK to sacrifice their life and time to develop a video game, they wouldn't easily find another job.
But nowadays, software is 1000x more important than 15 years ago, so good developers are much more demanded than before, and paid much higher than before, they know that their expertise is viewed as a valuable skill. To develop a good game, one needs to be able to write a solid code, read lengthy and complex documentations, fix bugs, understand optimization, but those who know how to do all of that, could as well just write software for finance, AI, cybersecurity, or any field which barely existed 20 years ago and pays 3x more than video game development today.