What’s stopping Taylor Swift from becoming a greater vocalist?

I know she doesn’t NEED to be a vOcaLiST. Her talents strongly lie in songwriting, no doubt. But one criticism that has always come her way is her vocals. “She can’t sing live”, “she’s not even that good” etc. I absolutely don’t have a problem with her vocals. However knowing Taylor, she has always taken criticism and worked on it and sometimes it pays off and sometimes, backfires. Point is, she seems to hear criticism. Knowing her grit and determination, it’s totally possible that she could have taken the criticism and emerged as the greatest vocalist of her generation lol. It just baffles me that this is one area where while she has shown significant improvement, she hasn’t gone ALL the way. Why?

Edit: I’m a fan of Taylor Swift! This isn’t a hate post. It’s just an observation. She has reacted or responded to any/all criticism before. She can’t write? Speak Now. Red was not cohesive? 1989. TTPD was too long? TLOASG is airtight. I only am expressing a question here. People, stop hating. This is meant only for discussion!