Pirates was one of Lego's best-selling themes, but one year they took it away and it didn't come back for a long time.
Refreshing the brand?
If TLG decides Bionicle needs a break, then that's what'll happen. I'm not saying it will, but it's a possibility. Ten years is a long time, and after so long, anything can become mundane. Even if sales don't drop, TLG might just decide that, for the good of the brand in the long-term, Bionicle needs a break.