They make too many of the bigger Bionicle sets, and all the sets are overpriced. IJ sets were on clearance a lot, doesn't mean they didn't sell well, just means they made too many, or that one store got too many.
I have never seen a smaller Bionicle set on clearance, never, they have always been the bigger sets. The smaller sets go on sale, but that's because they were too much to begin with.
It's why news of it's ending was so amazing, because it is a powerhouse, however it's clear they have run out of ideas because the limited 2010 sets there are are redoes of sets from 10 years back. LEGO probably saw it as time to see if they could do something new with the line. If not Bionicle can always return, and I have a feeling it will rather soon.