Canada

Housing is an easy example. One bedroom or bachelor's pads are, in my area, ~1200/month. Not the nicest ones at that price, but decent. You jump up to a two bed or a Ben+a den, and you're looking at 1800/month at least. At a three bed, it's close to 2500/month.

Even if you assume those are on the larger side for price jumps, if you're barely able to scrape by with two people in a bachelor's apartment or in a one bedroom, there's no way you can "afford" it solely by CCB benefits. Almost all the benefit is eaten up by housing increases alone! Then add on childcare, and CCB isn't enough to give those feeling like they're just hanging on wiggle room to raise a child.

Kids are an enormous financial burden early on, especially for the small things. Kids get sick a lot, so you need to have a job that will allow you flexibility, or else you'll lose money for unpaid days off for doctors appointments or to sit at home with them when they're puking.

Kids need daycare unless youre staying home, which is suuuuper expensive these days. They also have limited hours, which if you're stuck working a shitty job, you may not be able to make.

Even second hand, clothes are expensive, and with how fast kids grow, it's an expense worth noting.

All in all, if you're well off, yeah it may not be a big problem for you, but for the people that are already struggling, it's a large factor into why they're not having kids yet.