All of those were written from the start to be a part of George Lucas' universe, designed to fit and tie into each other. Bionicle and Hero Factory were not, and forcing them together would result in a disastrous Frankenstein of a story. Tahu Meets Furno would be a complete farce and irreparably ruin Bionicle's legacy. Hero Factory is a silly franchise, so it could do cross-overs, but Bionicle cannot.
The only way to avoid this is if the version of Hero Factory that meets with Bionicle was a totally different version, a reboot that fit with Bionicle's genre, but at that point it wouldn't be Hero Factory anymore.