And as you prove it here, sometimes we can identify them

Identifiable or not, the problem is listing vehicles that should not be there. This one is close to actors, so probably noticeable, hence why it could be considered as worth listing (hypothetically), but often those with low visibility are just in a background of a warehouse and so not worth including anyway. And that can even be applied to some identifiable vehicles: being identifiable does not mean it is worth listing, sometimes you take time to identify something that should just be deleted, and for which you could say "not worth listing" like some more difficult ones