27 Dresses

Jane Nichols (Katherine Heigl) has been a bridesmaid for 27 weddings. One night when she is attending two weddings almost simultaneously, she meets Kevin Doyle (James Marsden), who helps her get home but disgusts her with his cynical views of marriage. He finds her day planner in the cab they shared. Meanwhile, Jane's sister Tess (Malin Ãkerman) arrives from Europe and falls in love with Jane's boss George (Edward Burns) at first sight. Tess pretends to like the same things that George does to get him to like her. Despite of being in love with George herself, Jane does not reveal the truth and her sister's courtship progresses rapidly. Soon the new couple announces that they intend to marry in three weeks and Jane becomes the wedding planner.
The reporter who agrees to cover their wedding for the society page turns out to be Kevin, who writes wedding announcements under the pseudonym Malcolm Doyle. After looking at the contents of Jane's planner, he decides to use the contents as material for a piece on the "perennial bridesmaid" and hopefully be promoted to writing investigative pieces about "real" news.
Jane is unaware of Kevin's intentions. When he asks to interview her for his column on Tess, he gets her to try on all 27 bridesmaids dresses in her closet. He takes pictures of her in all of them and sends them with the completed article to his boss. As they get to know each other, Kevin begins to think that Jane is not as one-dimensional as he thought and asks his editor to hold his article so he can "fix" it.
When Kevin finds out that Jane is getting her sister's marriage fixed with the man she loves, he rebukes her. Jane agrees to one drink with Kevin and ends up getting drunk. Kevin and Jane kiss and have sex in the car. The next morning, the two go to a diner and a waitress recognizes Jane. Kevin's editor ran the article on the front page of the 'Commitments' section, despite Kevin and her settling to hold it for a while. When Jane finds out about it, she feels betrayed and is furious at him. Tess then gets angry at Jane for giving Kevin material about her, whom he describes as a bridezilla. The fight escalates when Jane sees that Tess altered their late mother's wedding dress to her own style â the last straw on Tess' string of lies to George and demands on Jane.
Despite the fight, Tess asks Jane to make a slideshow for her engagement party. Jane decides that George should know the truth about Tess and shows pictures of Tess with other men, eating ribs (as she claimed that she is a vegan, like George), holding a cat by the tail, and recoiling from George's dog (she told him that she loves dogs, but actually hates them) â in short, doing all the things she had told George that she never did. After that, Pedro, the child George mentors, tells the crowd that Tess had him clean George's apartment for money. George breaks off the engagement. Jane's friend points out that if telling the truth to George and breaking their engagement didn't make her feel better. The next day, Jane confronts Tess to apologize. She is still mad with Jane, as Tess believes that Jane resented her throughout the years. Tess reveals that the reason she stayed in New York because she got fired from her job and her boyfriend dumped her; she explains that when she met George she'd tried to be like Jane since she fell in love with him.
Later at work, George tells Jane that he appreciates her because she never says no. Remembering that Kevin once said the same thing as a criticism, Jane quits and admits she only stayed at the job because she was in love with George. She discovers after an experimental kiss that she no longer loves him and goes to meet Kevin. She announces in front of a crowd at a wedding he is covering that she is in love with him.
One year later Jane and Kevin are getting married. George and Tess meet again and a hope for a second chance shows. All 27 brides who Jane helped, as well as Tess and Casey (Judy Greer, her best friend), are her bridesmaids, wearing the dresses she once wore as their bridesmaid.

Question: Why does Kevin rebuke Jane?