Here is my reasoning. You can do the activities you mentioned in places that are a lot more comfortable (sofa), more social (cafe) or more beneficial (gym) than the driver's seat.
More importantly, I don't trust my brain's thread scheduler to drive with full attention and think about something else productively simultaneously. How many of us can say that they have never been in a dangerous scenario because they were lost in thought while driving?
More importantly, I don't trust my brain's thread scheduler to drive with full attention and think about something else productively simultaneously. How many of us can say that they have never been in a dangerous scenario because they were lost in thought while driving?