My guess is that this is because having kids is the status quo -- anyone who decides to not have kids is making a very conscious decision to do so, and is more likely to be happy in that decision. Some portion of those that have kids do so because it's just the accepted thing to do, regardless of whether they truly want kids or not.

Sure, credit card rewards are rip-offs if they're bad rewards, but it's not that hard to avoid those.

If you pay your credit card off at the end of every month (you ARE paying it off every month, right?) then the interest rate doesn't matter. And with something like Discover it's trivial to check how many points you've accumulated and either cash out to a gift card or just cash on your statement.

Anyone who doesn't take advantage of rewards is missing out.