Are women from USA scared of marriage?

Something has been bothering me a lot these days. Is it just me or majority of women from USA are scared of marriage. My 3-year relationship with my girlfriend just went down the drain after I proposed to her. It was a really great relationship so I thought, hey, maybe shes really the one. I prepared a very romantic proposal, informed her mom of my plan, but when I went down on one knee she turned me down. She said shes not ready to marry yet, said shes still building her career. Also said shes still not ready to have a family. Were already turning 30 with great jobs and has our apartment. I thought by now she would be. Does she just dislike the idea of marriage? Was it me? Im really confused right now.