Overweight Ford F-750 Plunges Through Historic Wooden Bridge in Maine
thedrive.com
thedrive.com
An alternative reason would be that the driver consciously disregarded the safety notice, perhaps thinking it overly conservative, or thinking that they could get through with only stress to the bridge that's not traceable to them.
But also, pay attention to signs.
American obsession of multi-ton metal chunks on wheels has it's 2nd order effects.
It's unlikely to be an excessively sized "big ass truck" driven by an office worker but rather a case of poor judgement by somebody who really needed a vehicle like that to move a heavy load so it ought to be filed with the various cases of tractor drivers who keep getting their vehicles stuck because they drive them in the wrong places.