Why won't my husband agree to have another baby?

I am having a hard time with my husband. At the end of 2019 I asked if we could try for a 3rd baby and he said he wasn't ready for another. I waited. Then at the end of 2020 I asked again and he said next year. So I waited again. As you can see, it's 2022 and I asked him if we could start trying this year and he said we will next year. His answer is always 'next year'. But when it is 'next year' he pushes it again. With our first kid, I had to wait till he was done with school. (Which I was ok with/understand.) With our 2nd, he wanted to wait till our 1st was older. So we did. And now, more waiting. Why do I have to keep waiting? Why is it up to him if/ when we have kids? It makes me so mad that it's to the point where I don't want to have sex because it's just a constant reminder that he doesn't want another baby. And yes, I do talk to him and ask him why and he just keeps saying he isn't ready. And when I bring up that it has been 2 almost 3 years since I first ask, he has no answer. I don't know what to do anymore.