People aren't breeding and I don't know why

People aren't breeding and I don't know why

I'm almost at 8 years on my current colony, we've had our struggles but now everyone's mood has been maxed out for 2 quadrums or so. I have 2 couples sleeping with their partners, it's been like that for a few years, and they've never gotten some lovin' a single time.

I wanted to expand my colony with children but I guess that's just not happening. (Although I'll admit it's not happening anyways because my couples are old infertile people, but still they're barely 50)