Because it's clear you're arguing from an emotional standpoint.

This is truly uncalled for. It's rude, and it's dishonest.

I've provided a specific textual analysis of why Sansa's book arc makes sense as character development and why her show arc does not. Instead of addressing these points, you keep fixating on my feelings and what you presume I cherish. (As if providing a textual analysis is somehow proof of emotional state, or as if being invested in something even means an argument is incorrect.) This is a truly dishonest discussion tactic, and if you can't stop fixating on what you presume my feelings are, this will be my last comment.

Adaptations make changes all the time

And people who consume media critique media all the time. People who make adaptations make choices just as the original author made choices, and all those choices are perfectly available for analysis and criticism. Critical analysis of media isn't beyond the pale--it's a totally normal component of the way people consume media.

Sansa is a frigging literary concept. She doesn't "need" anything.

And this is exactly the crux of the issue. In well-done fiction, in the context of the work, the characters are people. The characters do have wants and needs. They are realistic in that they are three-dimensional and that their personalities, not the whims of the plot, drive the action. One of the reasons Martin's books have been as praised as they have is that his characters act true to themselves, not conveniently for the reader or even frequently the author.

When you remove a character's development--when you gut a character's experiences and actions and personality and then just skip them to the endpoint because you realize you need them back where they were supposed to be--to glue the plot together, that's flat-out bad characterization. And in a story like this one, bad characterization is simply bad writing.

Sansa's not really a person. No one in this story is really a person. But within the narrative of a good story, all the characters are people. If you have to back out of the story and say, "it's just fiction," to justify a decision, that decision has failed within the context of the work. "This isn't real," isn't an argument; it's a surrender.