Why was the Canadian 4x100m team disqualified in the Olympic final?

Various news articles reported on the disqualification of the Canadian 4x100m team during the Olympic final.
Very few presented all the facts, thus creating an impression that they were treated unfairly.
The facts and rules are as follows:

• The athlete stepped on the inside line of their assigned lane.
• The rules state that an athlete stepping on the line on the inside of the lane will be disqualified

In the past the number of steps on or inside the line was considered. Why is the new rule so harsh?
The distance is measured 30cm from the inside of the lane for lane 1 and 20cm from the inside for lane 2 and outwards.
The 'real' line is actually 20cm to the outside of the painted line for lanes 2-9 and 30cm from the curb for lane 1.
This means and athlete stepping right next to the line is actually running slightly shorter than the total distance and already gaining an advantage.
There has to be a line somewhere and it is clearly visible and the athlete should not step on that line.