There is no rule that says that a player may not return any kicked ball.
There, I've said it twice.
It is the teams that are choosing the fair catch because they know the odds of returning a kick past the 25 yard line are less than 50%. They knew that last year as well, when only 6 teams averaged 25 or more yards per return (for a grand total of 6 TDs league wide). Now they have another option to be awarded the ball at the 25.
Or they could return it. No "legislation" has changed that.