Why do referees suddenly care so much whether or not the goalkeeper has a foot on the goal line during a penalty kick?

Question

During the Women's World Cup 2019, the Nigerian goalkeeper defended a penalty kick in the 75th minute only for it to be retaken due to the fact that she did not have a foot on the goal line as the shot was taken. Due to this, France went on to retake the penalty, score a goal, and win the match.

Nevertheless, last year, during the Denmark versus Croatia game, in the second half of extra time, Denmark's goalkeeper Kasper Schmeichel defended a penalty against Luka Modrić. And yet, if we see this image it's pretty obvious that the goalkeeper does not have a single foot on the goal line.
Shouldn't the penalty be retaken?
Why did nothing happen here?
And why are the referees so adamant about this rule in the Women's World Cup?

Answer 1

One simple answer: VAR.

As it is still a new technology, referees are unsure of the extent they should review decisions. In the past, when VAR was not used, referees were free of blame (to some extent) as the decision had to be made on the spot. However, as they are now allowed to review any major decision, they are now being criticized for not using it enough.

2018 World cup was the first major tournament with VAR active, the referee, Nestor Pitana, was obviously not used to it yet

Answer 2

In short: The rulebook has changed since the World Cup was played.

This years Women's World Cup is being played under the 2019/20 Laws of the Game which have some significant changes from the previous 2018/19 edition.

In particular, Law 14 Penalty Kicks now says that

The goalkeeper must have at least part of one foot on/in-line with the goal line when the kick is taken.