I can understand people not seeing a warning light, as most never look anywhere other than straight ahead, choosing the speed according to what feels right for the situation, or just following the one in front, mostly too closely.
Many years ago, a colleague had to look at his mother-in-law's car, as the battery had 'suddenly' gone flat. As he connected the jump leads, there was a little spark. Thinking the radio might be let on, he jumped in, to find the interior lamp on. As is usual in most cars, this is directly above the interior mirror. Yet mother-in-law had not noticed. She remembered she'd used the light about three days earlier. So that's three days without looking in the mirror.
It is not surprising that a lot of new cars have so many lights, and 'bongs', because drivers have no idea what is happening around them, or to their vehicle.
With any warning light, we need one on the roof too, to warn others to give more space.