Making characters unlikeable before killing them off?

I feel like this is a common thing in Greys, where a character that is pretty liked by the viewers, will all of a sudden have a storyline or do something terrible, leading up to their death.

Now I get this might not apply to every character, but take Lexie for example.

7 episodes before the plane crash, Derek leaves Lexie in the OR and tells her not to take out a brain tumor. Meredith comes in after to supervise, and Lexie insists that she can take the tumor out, even though the patient only consented to an aneurysm-clip (which I don't think Meredith knew). Despite Derek telling Lexie not to touch the tumor, she does it anyways and celebrates when she's able to get all of it. Then the patient wakes up and is no longer able to speak. And Lexie doesn't end up facing any consequences.

Same with Derek. He and Meredith overcome all their obsticles, only for him to suddenly leave for Washington in season 11, leaving Meredith alone with their 2 kids. And then proceeds to cheat on her, before getting killed in a car accident.

Although I think Reed and Percy were written to be these kind of arrogant characters mirroring characters like Christina and Alex in some ways, Reed jokes and disregards Izzie when she tries to tell her they keep George's locker empty out of respect for him. And while she has some good moments (defending April after she's fired), she is in a lot of viewers' eyes (and probably the writers) considered a disposable character that most fans won't miss too badly.

Now I know this doesn't apply to everyone. Heather Brooks (season 9 intern) was a great example of a lovable character just tragically passing away just as she and Derek were starting to form a mentorship bond.