"The one line that LEGO made and created themselves?" No idea what you mean by that. Bionicle is just one of MANY lines that LEGO created themselves, including City, Friends, Ninjago, Elves, Technic, Creator, and Nexo Knights. And contrary to your assumption that LEGO's success is "concentrated" in licensed themes, the truth is that licensed sets make up no more than a third of the LEGO Group's business, a status quo that has held steady for over a decade. Of the LEGO Group's five top-selling themes last year, only one (Star Wars) was licensed, three (City, Friends, and Ninjago) were non-licensed, and one (Duplo) was a mix of both. The LEGO Group's portfolio of non-licensed themes is far more successful today than it was before Bionicle G1 began! Clearly, it wasn't Bionicle's originality that did it in, nor is LEGO in any way biased towards licensed themes when it comes to what properties they invest in.
To be fair, Creator, City, and Technic are mostly based on real-life things. (Not that that means they're bad.)
I do however think that Bionicle might be the least derivative of Lego's themes, or the most original, if you will. Saying that it's the only one is not really accurate though.