What makes teenagers the first phase of raising children?

I have 6 and 4yo girls currently and keep hearing how teenagers are the worst phase of raising a kid. Jim Gaffigan has a funny bit about it.

What makes it the worst? I love my kids and spending quality time with them. But they are so needy it feels quite literally like walking around with a ball and chain. They also fight and whine about everything.

How could teenagers possibly be more difficult than what I'm dealing with now?