Wile this is disappointing to me, for I just paid for this not long ago, in the world of developers, it's not surprising. One has to make the most logical choice one can.
There is also two things to consider. Yes, a 3D game with a lot going on in it can take a long time to make. Just look at how long such games as Hunt and Snare or Sapphire Safari have taken, and both are so far form being a finished game. Few game makers what to work that long on a single project and not seem to have much to show for it.
The up side, is once you get the main maniacs working, the rest of the development should go much faster. Should. But, what may sound good on paper, may not work as predicted in real life.
The other thing is, with so many indie games being made, and the good 3D indie games either taking way too long for many to care about anymore, until it is finished, or the game just out right getting dropped, after a person took an interest in it and paid to support it. Just as what happened here.
With that happening too often, it is of not surprise you didn't get many sales of this, vs your 2D game.
Those wanting to support such 3D game are getting burnt out. Either from waiting for a project they liked to get finished, or end up watching it get dropped eventually. This makes people not want to invest.
So, is in part why I am not surprised few wanted to buy this 3D version of the game, without knowing it's full progress. I paid for it, when I did, after you posted Chapter One is done, making me feel I can trust that you are still working on it, and it not be just another dropped project I was hoping to see get done.
Reminds me of what I told Shout Factory, who was selling the MLP FIM cartoon, didn't want to bring it out on Blu-Ray instead of DVD. They said their DVD sales are not good, so they not going to bother with Blu-Ray. I told them, your sale of DVDs are not good, for it's old tech, and people want them out on the much better looking Blu-Ray. Why they going to buy it on DVD first and again in Blu-Ray later? They won't. They not going to buy your DVDs when they want it on Blu-Ray and are waiting for them insted.
They last told me, no parent is going to buy a Blu-Ray player for their kid. I told them, what you think most modern game systems play for disks? Blu-Rays. And many adults like the cartoon also. They still to this day, have not got them out on Blu-Ray.
Is just the way it is.