My current car was even built around that stupid idea that turn signals are for while you change lanes.
It has a feature called “blind spot safety”. Basically if I’m on the interstate and I put on my blinker to let people know I want to change lanes, if there’s a car in the left lane it turns down the music and beeps a loud warning at me.
In other words, it treats me turning on the turn signal, when the lane on that side isn’t clear, as a danger scenario deserving of a warning. It’s the same kind of warning as the collision warning.
So basically, it’s built on the assumption that me turning on my turn signal means I’m already turning the wheel to go there.