I just want to get this out there and express it without looking at my notes.
For one, I think Grete is the main character of the story. Her reactions and her emotions might be even more of a focus than the thoughts that Gregor has. They're the ones that most influence the story. Second, I think the metamorphosis in the title refers to her change from timid young girl to what the parents see as a capable young woman. At the end, her parents witness both her body and personality are different from when the story starts. Through the change that afflicted Gregor, she is the one who was changed the most. I don't see another reason why that would be a strong focus at the end.
Lastly, and to get to my title's point, the worst part about the story to me is that after all the growth she has gone through, her parents' first thought is for, presumably, stability in the form of romance; for their daughter to be paired with someone. We're told how Gregor was planning on sending her off to school despite whatever drawbacks that might have for the family. In the condition they are in at the end, she would be able to do that, and the hopes of Gregor for his young sister (and I'm assuming these are hers, as well) could be fulfilled. Instead, the parents think to romance, and in the context of the era when this book was released in, I'm sure they only have this in mind as a form of financial stability.
by AllHallNah