People think money is enough because they look at their lives and think 'how could I afford kids? Clearly I need money to do that.' and they don't think 'if I had extra money, would I spend it on someone else or on myself?' and the majority of people choose spending it on themselves instead of that potential child someone else.

Those people often don't even consider the time cost either. Which makes sense, if reason A is sufficient to say 'no' then why continue dwelling on other reasons? But even if there was more money and they were willing to not spend it on themselves, they now need to accept giving up roughly 90% of their non sleep/work time to someone else as well. That's not giving away something new you didn't have, that's giving up something you've been using and are accustomed to having.