I think there's multiple reasons as to why people don't really get married in their 20s and 30s anymore...
1. Women are more career minded.
2. High rate in Divorce, so people want to be sure of their decision before jumping into marriage.
3. Fear of commitment. People just want to have fun when they believe they can.
4. Marriage to younger people aren't necessarily seen as a true commitment since they are able to divorce so easily. Marriage isn't taken seriously anymore.
5. Some people now just aren't interested in marrying. Being together with their significant other and have kids and a family with that other person as if they were married though.
6. Lack of good role models that have been married.
7. Too much pressure looking for 'the one'
8. Not the 'right time'.
I'm sure with more time I would be able to think up of other reasons.
Anyways, my boyfriend and I have been together since high school and have been together for six years. We have plans to get married in the future, but definitely not in the next few years. We are able to grow and learn from our mistakes with each other and see how we react after a fight. We aren't financially stable right now, nor have we finished college. So right now isn't the 'right time' for us to get married. When we're ready, we'll get married. Right now, we'll just learn about life and travel and do things we wouldn't be able to do once we settle down and have children. (not saying we couldn't when we have those kind of things, it would just be more difficult!)