I think characterization moving forward is something that is actually more or a double-edged sword than people think. Yes, it's great to see characters grow and change as well as their journeys. However, it is VERY easy to ruin characters and take away what was good about them.
I'll use one from a recent book. Ironically, of course, by his creator (who has the right to do this)
To quote a Vulcan proverb, "I ****ing *HATE* what they did with Xyon of Calhoun." I was really invested in the Kalinda/Xyon relationship and felt what they did to him was just plain vile. It left me feeling more than a little unhappy about the direction of the book series as a whole.
People become very emotionally invested in characters and hate when they are changed in a way they feel isn't organic or in a way that seriously hurts their investment. It's why shipping wars exists in other media. If you were really invested in Worf/Deanna Troi for some reason, Riker and Troi might bother the hell out of you.
It's human nature to want to have characters remain consistently the people you believe them to be.
There's a difference between some fans of a character not liking a change made to that character, and a character being ruined. Heck, even just talking for me personally, I can acknowledge that there's a difference between me not liking where a character ends up, and me thinking that character is ruined. You have to separate your enjoyment of something from your opinion of its quality. "I like it" isn't the same as "I think it's good", nor is "I don't like it" the same as "I think it's bad".