Waiting Longer to Marry

On why Americans are waiting longer to marry. I think they are forgetting another obvious reason: life expectancy. We are living longer, so as a percentage of life spent married vs. unmarried, I would think the numbers might be similar. At least in my own head, marriage seems like a big step, a step from which you do not return. So what's the rush? Especially because I plan to live into my 80s and work into my 70s.