Rubble, broken glass, bits fallen off cars, the wands that cars have knocked down, crap thrown on the road which all end up there, bottles and cans, the aforementioned utterly deadly surface type interfaces, the camber, the way that the snow is pushed there by buses or clearance etc. etc. etc.
Professionals just avoid the side of the road and take a lane which they are entitled to do by law as the side of the road is not designed for traffic. It’s for car traffic effluent.
