Why does Mrs. Jones close the door before Roger has the chance to say "thank you" in "Thank You Ma'm"?
Mrs. Jones closes the door on Roger because she is does not want to seem sentimental. She also wants to get rid of him as quickly as possible because he has reminded her of some unpleasant parts of her own past.
Mrs. Jones is an older woman who stops Roger from trying to steal her purse. Instead of turning him in to the police, she takes him home and has him wash up, then cooks him dinner. At first he is surprised, but then he comes to appreciate her. She tells him she has done some bad things in her life too.
"I have done things, too, which I would not tell you, son—neither tell God, if he didn’t already know.” (p. 3)
The boy’s attitude completely changes under Mrs. Jones’s tutelage. He becomes respectful and trustworthy. He even offers to go to the store for her. After she cooks him dinner, she gives him the money for the schools he wanted to buy—the reason he tried to steal her purse. She tells him not to try to steal from anyone else.
[Shoes] come by devilish like that will burn your feet. I got to get my rest now. But I wish you would behave yourself, son, from here on in. (p. 4)
When she closes the door before he says thank you, she has reached her limit. She did care about the boy, and saw him as a lost soul. She wanted to teach him a quick lesson, because perhaps no one did for her, but then get rid of him as soon as possible so she would not have to think about her past.