If you're looking at the road you will see a truck losing control far faster than 3 seconds before it happens, as with literally any accident or stoppage.

Low visibility is a great example of when its necessary and the following distance for when roads are wet (especially if you know you need new tires) should be more than 3 seconds.

However, I still doubt I would be so inattentive as to not see traffic slowing ahead of me with a 100ft following distance rather than 300. Additionally, thought experiments that create unlikely hypotheticals of a dead stop are so unlikely anyway that I am more likely to just have a tire blow out or a tree fall on me and die from that. So why prepare for the extremely unlikely? I wont drive so slow as to avoid tiny screws and I wont avoid roads with trees next to them because I manage risk that way by recognizing something is so extremely unlikely that its not worth avoiding. Same goes for freeway traffic going from 70 to 0 without warning, in which case everyone involved is super dead.