I suppose one becomes ready to move on from the self-indulgent lifestyle and start something else, something harder but ultimately much much more rewarding than a night on the beer, or a line of coke.
While I'm delighted that you are happy with your choices, I think "self-indulgent" is an unfortunate choice of words.
I have three kids. Always wanted them, so if for whatever reason it didn't happen for me I probably would feel that there was something missing from my life.
I didn't get the "bam!" moment at birth with any of them. Maybe because I had C-sections and the usual hormones weren't flooding around, maybe it wouldn't have happened even with no C-section. In fact, I only got a "bam!" moment with my first, a few weeks in. The other two the love was a slow burner, over the days and weeks after birth. At no point have I ever felt "ahhh, now life makes sense, now I am fulfilled".
I'm happy with my choices, but there's certainly a part of me that envies the child-fee life of some of my friends. How would I feel now, if I hadn't been 100% convinced I wanted children before I had them? Maybe I would feel the same way - the same slow burner love would have happened, and I'd envy the child-free life but not so much that I'd want things differently.
But I f*cking doubt it.
I'd probably regret having children. And I'd never be able to say it publically so I'd internalize it at take it out in small ways so that my kids would grow up to be baggage filled little ****s. So what I'm trying to say is, if someone isn't 100% convinced they want kids, absolutely don't do it. There's nothing self indulgent about concentrating on your own life. We're all born, we all die, and in between we try to make the world a better place when we leave it than when we entered it.
Having children doesn't necessarily mean that you'll end up a net contributor to the world, and it is certainly less likely if you weren't convinced you wanted them in the first. So I say don't listen the "I was a self-obsessed **** who never wanted children before my surprise baby came along. I had some sort of religious epiphany on the day of the birth, and I now feel so connected to my purpose in life, that I cannot understand how I even existed before".
Because if that happened, well, fantastic for you. But for every one of you, logic dictates that there are five others who realise they just set fire to their lives and there's no way back.
And incidentally, I'm retiring to Florida when I'm 70, so I'm absolutely not counting on my kids to take care of me. I hope they end up travelling the world without even thinking about having to be close to take care of their parents.