There are many different reasons why people write poetry. Some write because they like to share their words with others, some write with the hope of getting published. Some think they can make money by writing poetry (teehee, if only they knew!)
Some people use poetry as a way to explore their thoughts, to get a better handle on what they think about issues. Others write poetry as a form of personal therapy.
Sometimes the reason is to impress someone, or to let them know how you feel. Sometimes people write to entertain or to teach.
All of these reasons are valid reasons for writing poetry, and sometimes the reasons blur somewhat, like when a heartfelt poem written as personal therapy can reach out and touch other people. Poetry, when it is good poetry, tends to focus on the particular, not some undefined thing, but at the same time being universal, so that readers can see their own meaning in it.
Poetry can be written to amuse others, such as limericks written about people you know, or as lines in a greeting card for someone special. Sometimes you may write a poem with no intention of ever sharing it with anyone, only to find a certain somebody who your words seem to have been made for. Connecting with people through your poetry can bring an extra dimension to a friendship or relationship.
Try it, you may be glad you did!