That is a good point but it seems instructions for ground vehicles seem to really stress this. For example this one: https://skybrary.aero/sites/default/files/bookshelf/1003.pdf

Says at pag 9:

"While driving on an aerodrome : Clear left, ahead, above and right

Scan the full length of the runway and the approaches for possible landing aircraft before entering or crossing any runway, even if you have received a clearance."