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.