In many large and major markets, the local morning news show on a Fox O&O or affiliate is the most-watched TV program in that market between 7 and 9 A.M.
It's my understanding that this is not the case at KTTV-11, and that "Good Day L.A" badly trails KTLA-5's morning show (which I understand is top-rated in it's timeslot) and may also trail one or two of the network morning shows.
That may be the reason for the changes.
As for Jillian, I first saw her in October, 1999 one morning while on vacation in Los Angeles and watching "Good Day L.A." on the hotel room TV set. My then girlfriend and I turned to each other and quickly agreed that her style of weather reports would never work in our hometown of Boston.
For a number of years, Good Day L.A. and KTLA's Morning News usually trade the top position in their timeslot. I'm not certain on who leads between the two at the present, but I believe Good Day L.A. is doing considerably well.
Lucey and Reynolds aren't exactly the best of friends, and KTTV's news director is still fairly new (he's from sister WTXF in Philadelphia), so I'm guessing when contract time came, he wanted to clean some house. Jillian, for better or worse, is kind of the draw to the show, so that's why she's staying, albeit on a limited basis.