IME children that use a buggy 'late' tend to be children from a non-car owning family.
We had to make every journey by foot for at least the first mile (the distance to the bus/train station). Even if we then got on a train/bus, we'd often have to walk another mile at the other end, do whatever we'd gone for, walk back to the train station, go back on the train, then walk back home after a full day out.
Like I said before, anyone with a car would have simply driven door-to-door. We may have taken DD's buggy along when she was 4, but she still would have been walking half the time!
As for the thing about it being for the ease/convenience of the parents - well, yeah, to some extent, it was. I could have made her walk, however long it took, however much shopping I was lugging with me, whatever the weather, however much whining. It was a battle I chose not to have. DD walked when she wanted to, and gradually she got more stamina, and by the time she was 5 she was able to walk everywhere we went. Including the 4 mile round shopping trips - though we still take the buggy for the shopping. No luck so far in making that walk