So many people wouldn't think twice about deciding to drive because the walk was going to be long or late and they have a four-year old, but are still quite happy to judge people whose only wheels are on a pushchair, even though the parent with the pushchair is essentially making exactly the same decision (opt for wheels over a certain distance or later on).
Four is exactly the borderline age when this sort of judgement happens and the reason not everyone agrees is because it is a borderline age, and the right decision for one four-year old won't necessarily be the right decision for another. Even amongst non-driving families - just because one four-year old is fine with the journeys the family makes on foot doesn't mean every four-year old will be.
How nice for parents who drive that no one looks at them, after they've driven two minutes to the nearest shop when they could perfectly well have walked, and judges them for not making their child walk (or walking themselves) - it's just seen as absolutely ordinary.
Why does it have to be all or nothing for a child that age? People with cars can take their kids to events that last all day and involve lots of walking, because they can drive home at the end, but people without cars should not because their child might be seen in a pushchair for the last leg? Seriously? That child should miss the event but children whose parents drive don't have to?
The four-year old who gets into the car tired at the end of that day is being coddled just as much as the four-year old who's allowed to sit in a stroller at the end of a long walk or a long day - it's just it's not seen as the child being coddled because the parents are coddling themselves too.
It's vanishingly unlikely to be necessary for most five and six year olds, and even quite a few four-year olds will be fine with the scooter option, but if a parent feels that it's useful for them to have a maclaren or whatever as a backup option for a four-year old, IMO that's their call.