Because you can’t. You cannot change anyone but yourself
I had a couple of fixer uppers before I married my first husband, then I spent 12 years in a bad marriage before I learned this.
Then, I looked for someone who I didn’t have to fix, and he was the best thing in my life. I am still a fixer, and I tried very hard to avoid that in that relationship.
If you think you have a fixer upper, she either doesn’t want fixing, or… she wants to have an excuse to fail at things - she could have “taken your advice” but you made her mad tends to be the pattern in these cases.
Not to toot my own horn, but I recommend reading this