I wonder if it's at least partially because in the UK stop signs are pretty much non existent. I have only ever seen a handful in my life and people don't have this ingrained understanding that you absolutely have to stop at them and look around before moving - it's just a weirdly shaped give way sign to them.

They're typically only used in situations where you actually do need to stop in order to adequately see what's coming. In the last city I lived in, there was one single stop sign, and we used to say that it was there just so that learner drivers could be taken past it and tested on it. Now I live in a small village and there is a genuine blind junction with historic buildings right down to the pavement, and there's a very appropriate stop sign there.

It is a test failure if you do not stop the car and put on your handbrake in the UK. It is made quite clear what you are supposed to do.

People just can't be bothered to actually stop.

Yes, of course, but I think we have to acknowledge that it's a very uncommon sign in the UK, and the fact that you almost never come across it in your day to day driving might make you numb to it - and in like the car in the video, just blow right past it. Maybe someone who interacts with Stop signs every day and has to obey them on a regular basis wouldn't have done that.

I don't know of course, this is pure speculation

Yeah its terrifying. As he says "They are reckless & can see the main road is clear", blind spots are scary.