Also - no kids - huge variable for FIRE obviously, but perhaps less obviously ALSO a huge variable for life's purpose.
Something I've seen in my friend and family group is that a lot of couples hit a point where the answer to the "what's the point of all this?" is to create a family. Sorry if that sounded crushingly heteronormative - but this also includes gay folks in our life.
Not suggesting that everyone should have kids, or that the childfree people are somehow bad, or even that it's not a rational choice to go childfree. All good to those thinking that way.
But. If your conclusion is that love and connection is what life is all about (assume Maslow's lower levels are covered), then having children is possibly the magical thing missing. Not necessarily for everyone. But it's a game-changer for many of us and provides some incredible direction and purpose (as well as very low low's and constant anxieties).
Having children also can change your priorities in how you spend your own life. For me personally, I'd want my children to see me working hard at something; having adventures; building things; changing things for the better. All of that can happen inside the typical FIRE life. But as he points out, your life gradually disconnects from things if you're truly independent and separate. And unless your wealth is large enough that your children will also be FIRE, you really want them to learn from you in how to navigate "the typical world" of jobs, managing finances, etc.