We own two pretty small strollers for kids of different ages, but for the sake of argument...
Let's say a family owns one stroller. It is large (one of those top-of-the-line models), and it was a gift from a registry. The family usually stays in Brooklyn, but occasionally rides the subway into Manhattan.
You want a family to buy a second stroller just to save a few inches on those occasional trips?
Or let's say you're a parent or nanny responsible for watching a child. You don't want to stay home all day, so you pack the supplies necessary to travel around and do stuff. Which requires space to hold things.
You want that caregiver to travel in a taxi all day instead of the subway?
It's easy to judge from afar. Life with kids is hard and expensive and complicated. Becoming a parent changes your perspective.
Apparently to the perspective of "fuck everyone else". These little fold up strollers are not that expensive, and a friend of mine bought one for when she would take her baby on the bus. Or, as someone else suggested, take a taxi/Lyft/Uber.
Just because you're a parent doesn't mean everyone should bend over backwards for you.