Afford to have one are the ones who don’t have any desire to, and the people who do have kids would be seen as not being able to afford it.
Sure this is a broad statement but in general it’s more cultural than successful. Society has been trained that work success, and more recently personal wellness are more important than anything else. Having kids is often a deterrent to either of those.
Kids are a sacrifice and up coming generations in general aren’t finding much worth sacrificing for.