When we had our DC, we weren’t big earners, so we stopped at two. My friend, who was a doctor, married to a doctor, had four. Their income was much higher and more reliable than ours.
There were no top up benefits years ago, it was a case of we lived on what we earned. As @Strawberrycheesecake7 says, larger families are fine for those who can afford to support them, even more so now with the dearth of social housing.