So Lego's has had come up with good marketing techniques and some really bad ones. Keep in mind this is not insulting any of the themes
The reason why this theme failed is because there is noting fresh about this theme. No new pieces, no new ideas, just a bunch of what we've seen before in Water themes.
Yup, action figures based off a weird TV show. People weren't ready for this style of barley Lego like figures. When I bought these guys I didn't even know there was a show it was so unpopular.
This theme is almost like certain Racers sub-themes in the past only its own theme. Most of the aspects of this theme were actually pretty good all they needed to do was come up with design elements and a little more back story this theme could have been better then the dying theme of Racers.
Lego tried to bridge the gap between Duplo and System. But seeing as this theme was so similar to normal Legos and a lot of kids would just want the cooler System stuff.
This theme failed because it came out right when the beloved Bionicle was being discontinued. People automatically assumed that Ben 10 was replacing Bionicle. People also didn't like the 15 buck a figure price for a figure with barely any pieces. Thus the theme did not succeed.