I think it's not entirely true that thieves don't want to push the bike away. Some are happy to push a bike with one locked wheel through town in daylight. Some want to ride away, some sling it in a van.
Perhaps. Though I guess someone pushing a bike with a locked wheel / missing wheel* / no seatpost* / missing pedals is more likely to arouse suspicion, and they know that. They would arouse my suspicion were I to see them. However, I agree that if a thief has a van, there's little one can do.
*I remember when quick release was a new thing, cyclists would park up, remove their their seatpost and take it with them, and sometimes their front wheel too, because locking skewers hadn't been invented yet.