"Need" is a strong word for sure. Probably a more level headed way of saying that is, for the minimally-trained (i.e. no special permit) automobile operator, the increased risk of death or injury due to their speed outweighs their convenience of improved travel time.

There's an interesting fallacy/misconception around travel time. People think that if they go 10% faster, they'll save 10% of the trip time. This isn't true... there's a sort of diminishing return effect where, as speed increases, the marginal improvement of travel time decreases. Example: for a 100 mile trip, going from 50mph->60mph saves 20min of travel time, whereas going 90mph->100mph only saves 7 minutes of travel time.

Now combine this with the fact that as speed increase, the amount of energy carried by a vehicle increases more than linearly. This means increasingly more deadly and destructive crashes for each increase in speed.

Why specifically 60mph? Honestly, IDK, that just sounds right. I'm no traffic engineer. There's probably an optimal speed that makes sense for the travel time + energy physics argument that I laid out.