Season with the Ingalls leaving Walnut Grove

What was the reason for writing out the whole family in season 9 (I think..the one where the Carters move in)? Was it that Michael Landon wanted to work on other things? Did they want to take the show in another direction?

I like some season 9 episodes,but think season 8 should of been the last season.

I think season 9 could have succeeded better if it primarily focused on characters we already knew and loved, like Laura and Almanzo, Nels and Harriet, Willie (and his new wife was cute), Doc Baker, and Revd. Alden and Mr. Edwards. I think they brought in too many new characters. I would rather have seen Laura and Almanzo move back to the Little House instead of into their big boarding house.