I think that the OB6 and P6 got more hype initially because they built on their respective classic Prophet and Oberheim sounds. The Trigon is a synth that kind of gets Moogy, but it also kind of has its own thing.
I also think price comes into play. Had they keep the 6 series around $2,800, I think they sell more. But if anyone is considering a 6 series, well the P5 is the same price, and now we have the OB-X8 desktop in the same price. Sequential have crowded their own field a bit here in the $3,500 price range.
Anyways, I actually played a Trigon in a store recently. I really enjoyed it and thought it sounded great. I got some nice, searing, in-your-face sounds sounds out of it that I don’t think I could have gotten from the other 6 series. I love the interface of the 6 series, and this one is somehow a little better yet. It begs to be tweaked. Just first impressions of course, as I only spent so much time with it, but It is another great synth by Sequential.