I know this Engine since A5, then I bought A6 too but then I stopped. I think the main reason is globally the fact that there are still too many things at the old state of a few years ago. Not only the Visual things like the homepage, forum etc. I also mean those things like licensing questions..
Still only open source sdk, this is not really modern. U could expect to receive money for the sdk If it would be really one of the big engines. As a fan I know that the Acknex Engine is a big thing. But as a hobbyist programmer, it gives me the feeling of "outdated", it's sad yes, but other engines give also more the Welcome to this Engine effect. We are talking about an engine who's goal was and probably will remain to open the game development door for Beginners and give Professional ones the chance to be more productive with less time needed. So when I use it, I will think nice for hobby, then when I see that this project is getting important to me and I want to get something in the Enginge that hasn't been aready done, I use the sdk. But if I should add to the time I'm spending to "improve" the engine, money and maybe be thankful for havenig this opportunity I see what others engines are available in the world. And as most Engines today has built in scripting in Lua,Python or similar and often you see Enginges with .Net wrappers ( which means chances grow up to develop games in your prefered Language, even as a hobbyist I don't bother to much with risks in sense of performance impacts) I don't get that easy fascinatet by this Enginge as It was in 2001 where there haven't been so much competitors as today (and not that much hobbyist programmer like nowadays)

but i love this Engine and I still get back seeing what others do with it hehe