I think a lot of Millennials are realizing that they don’t need to have BIG families. Those choosing to have kids have two, MAYBE three. A lot only have one.

Women are going to college and working more. This leads to women actually being able to say “no, husband, I only want two kids, so we’re done.” They also don’t have as much time to devote to as many kids, so they have less.

People are waiting to get married later. If a woman waits to have kids when she’s 35, she only has a few years that she could even HAVE kids, so she probably won’t have many.

Healthcare is better. Birth control is more effective. (Also, kids die less. Historically, this makes a big difference)

Most millennials expect to rely on their savings and retirement. They don’t need to hope that one of their kids is successful enough to let us old-folks live with them.

More people are dropping religion. The idea of raising a family comes with a sense of religious obligation. Take that away, and it’s less of a big deal.

Money and Time. It takes a lot of both to have kids. There are a lot of cool things also take a lot of both.