>>116103004I think a lot of factors are part of it and I'm only speaking for America. I don't know how it is in other western countries.
Economy - Living is expensive and children even more so. In the U.S. having a baby in a hospital is $3k-$8k, most jobs don't have paid maternity leave so you have to choose to be out of work without pay or go back to work to pay those bills. This leads to needing childcare which is $9k a year on average. Having children on your insurance takes a larger percentage of your paycheck as well. The current system we have does NOT promote and support having children yet govenments punish and try to take away abortion. No one cares after the baby is born. So it's no wonder less people are having kids.
Technology - it's simplified life. We don't have to go through as much physical stress and instead we get more mental stress. It's spoiled and crippled us.
Life expectancy - Longer than it was in the past. We're healthier (sort of. Aside from fatasses) and even though our healthcare is laughable, we're still able to take care of ourselves better than our grandparents and great grandparents. It makes sense that we take more time to grow ourselves instead of being forced into work at 15, married with kids, and needing to pay bills.
Longer Education/socializing: When we graduate high school, we are just now experiencing life on our own and living by our own rules as individuals for the first time. This takes years to adapt and figure yourself out. You make the same mistakes you do as a teen but you don't have your parents/teachers/adults to bail you out or guide you. It's a whole 'nlther learning curve where you have to learn how to manage yourself. This isn't adulthood, this is second teenhood.
And finally we value childhood/nostalgia so much we don't want to leave it and it's socially acceptable.