Gabriel, you argue that there are too many 3D engines for BlitzMax,
No, I didn't say there were too many. I said there were several already available. Since there are already several, I said it's debatable whether it would be worth the author's time and trouble to support a language where most of the users who want a DX9 3d engine are already using one.
If there were a proper Direct X 9 engine for BlitzMax, I'd probably then buy it and program in BlitzMax, which is not the case ATM.
But it is the case at the moment. There are several high quality DX9 engines available, two of which are $100 cheaper than this one, and you're ( apparently ) not using those for free.
In my opinion the author of this engine is doing the sensible thing and concentrating his efforts on the people he is going to sell most of these to. People with Blitz3D who want DX9 features and Blitz3D syntax.
If you say you would buy BlitzMax to use this particular engine, I have no reason to disbelieve you. I just think you're in a very small minority.