There is a profound amount of entertainment and education at our fingertips, much of it available literally at all times. This includes adult entertainment, so it's easy to alleviate, uh, "needs". A lot of kids in the past came about from boredom.
Also, because of the access to information, a lot of people realize that raising a kid is, for most people, kind of a sucky job. I love my son and would do it all over again, but the actual job of parenting has a lot of boring stuff that pushes me back into social spheres with people I gladly left years ago. There are some people that love the job through and through, but I just don't think most adults are like that. And we can easily understand that as an adult now. Plus the pressure to execute perfectly is intense. My parents had me, my mom carried me around until I was school age, and then basically my life was my own after that - they cared about me and were good parents, but they only vaguely were paying attention to me (I was a 3rd child and generally good kid, so it was easy). GenX experience through and through. These days? My son is in high school and the insane rat race for college is something my son and wife and I are just saying "no thanks" to. He'll go somewhere and figure something out, but kids are literally spending 60-80 hrs a week on school and "extracurriculars". Too much pressure!
Really, there are just all kinds of factors now present that all push down the birthrate.