Strollers are a rare sight because they are a massive PITA.
I live in London and, like a few other mums - and dads - hardly ever used a stroller until my kid was well passed two years old. Whilst this is comparatively abnormal in London it is typical in Tokyo.
There are PLENTY of small children out on the streets of Tokyo, you see them on bicycles and, of you look closely, they are being carried ombushite style behind or upfront in slings.
Just because the Japanese don't have the same senseless attachment to strollers that the rest of the Western World have doesn't mean there aren't any kids around.
Strollers and prams are not the way to measure how many kids there are out and about.
I can see the baby carrier point gets made later, but it is almost an afterthought after the statement made in "Understand".