Prayer is so personal. Some people don't like to have any structure at all. It just wells up in them. But I love words. And I love God through words, so having a written prayer seems very natural and spiritual to me.
I've probably told you this, but the first church I served (I couldn't say MY first church) was not too "pastor-friendly", one might say. Right out of seminary, I was really trying my best. And each week, along with a sermon, I wrote a pastoral prayer. I slaved over the phrasing, and the words, and the images. It took a long time. Then during a session meeting one old codger - I mean elder - looked at me in disgust and said, "Some preacher! Can't even pray without reading." Now, looking back, I wonder if he COULD read. But at the time I was cut to the quick. It seems to me like criticizing another person's prayer style is something only Jesus could pull off.