Edit: "Afford" might not be the best term to use here since it relates to money mainly. "Capacity" might be slightly better.
Financial viability is improved with children (they start to contribute once you get past the first few years) – other animals like dogs, not so much.
Existing time and attention focuses can much more easily integrate children (like dining out? Bring your children!) – other animals like dogs, not so much.
Indeed they could. Most painfully, the child figure includes things like the cost of keeping a larger house. Yet in reality a child couldn't care less how big or small of a house you have. Hell, early North American settlers used to live in tiny, one room log cabins and raised like 12 children in them just fine. If parents choose to live in more luxurious accommodations, good on them, but if we are being honest that is an adult cost to satisfy adult desires, not a child cost. The cost to support a child on what is actually necessary to support a child is only a tiny fraction of that.
But let's say, for the sake of discussion, that the figure is irrefutable. A big difference is still that the child starts to contribute after the first few years. The outflow may be $240k, but there is an inflow to offset it. Unless you are an evil parent who locks the kids in their bedrooms until they turn 18, a net gain would not be unexpected.
While there may be individual dogs out there that could have the same said about them, in the typical case the dog can't offer anything to contribute, even if the dog wanted nothing more.
Studies that focus on what it actually costs to raise a child – not what it costs to raise a child and stroke parent egos – suggest that it is more like $4,000 per year to raise a child. So at this relatively young age are only in deficit by a few hundred dollars after a year. However, their capabilities ramp up quickly from there. If a teenager is only able to contribute $3k worth of value or less per year, you have failed them miserably[1].
[1] Or they have some kind of severe disability. That is the dice you do have to roll, but is statistically uncommon.