Castle nut and cotter pin missing from steering linkage suggest either neglect (incomplete reassembly after some work) in maintenance or sabotage.

Commercial drivers are supposed to do a pre-trip inspection before accepting the vehicle for the run. But even in the truck driving school I attended it was rarely given more than lip service so that one could pass the test.

(Of course most of the driving students hadn't the faintest idea what they were looking at and therefore no idea what to look FOR beyond tire tread depth.)