I thought the 3rd one was supposed to be the last one. I've only seen the first 2. Should see the 3rd one eventually. I thought instead they would do 3 focused on the cat, with the rest of the cast I guess as minor background characters.
I guess if they had the right writers who are very creative and or brought in some, switched some out the franchise need not loose steam. Though there is no reason why some of the movies could not focus on say the cat for some, the donkey for others, or other members of the cast.