It's also not abysmal, either. In fact, it's how G1 ended.
And we can only guess as to why until more evidence comes up, because we have nothing to go on except Lego's official statement.
And they didn't, they said it sold average. They could have just said nothing, like they normally do. It might have simply been on a downward trend, or even just not growing in popularity like they wanted it to.
Prove me wrong by providing some.
And there are probably countless potential reasons why it didn't, any of which could have been the ultimate cause. Again, there's really no proof that Lego lied about Bionicle's sales, so there's only speculation; and based on history, Lego was just trying to keep the line viable for the future.
You act like Bionicle is dead forever when your only justification for thinking that is that G2 was cut short. Promoting that mentality will only reduce the chances that it comes back with the right team behind it who's going to use their hindsight to make a really good reboot. You're basically doing the antithesis of what Faber's doing, which is counterintuitive to this thread's topic.