It's the same with those signs that light up with the message that there's something loose or an obstruction in the road ahead and warning you to slow down to 50mph.
When you see one of a warning sign "Queue Ahead, Caution" at 2am on an empty M25 and slow down, but a couple of miles (and other, blank signs) later there's absolutely no sign of a queue it generates a "Cry Wolf" reaction.
I had exactly that happen, with the result that, a couple of months later, on the M27, about 10pm at night, light traffic, free flowing, dry conditions, I saw the same sign and thought "Yeah, right".
So when, about half a mile later, I found that a car had shed a load of stuff off its roof-rack, I just had to hope I had picked a clear line because it was way too late to slow down and trying to do so would probably have destabilised the bike if I had had to try to manoeuvre.
Had it said "Debris on Road" or similar, I would have definitely slowed down.
So to expect that they get things right on "Smart" motorways is too much to hope for